Appeal to the Court of Tax Appeals En Banc

Appeal to the Court of Tax Appeals En Banc is provided under Section 18 of Republic Act No. 1125, as amended, which states:
SEC. 18. Appeal to the Court of Tax Appeals En Banc. — No civil proceeding involving matters arising under the National Internal Revenue Code, the Tariff and Customs Code or the Local Government Code shall be maintained, except as herein provided, until and unless an appeal has been previously filed with the CTA and disposed of in accordance with the provisions of this Act.

A party adversely affected by a resolution of a Division of the CTA on a motion for reconsideration or new trial, may file a petition for review with the CTA en banc.
Meanwhile, Rule 8, Section 4, Paragraph (b) of the Revised Rules of the Court of Tax Appeals provides:

RULES 8: Procedure in Civil Cases
SEC. 4. Where to Appeal; Mode of Appeal. — xxx

(b) An appeal from a decision or resolution of the Court in Division on a motion for reconsideration or new trial shall be taken to the Court by petition for review as provided in Rule 43 of the Rules of Court. The Court en bane shall act on the appeal.
Under Rule 43, Section 1 of the Rules of Court:

RULE 43: Appeals from the Court of Tax Appeals and Quasi-Judicial Agencies to the
Court of Appeals
SECTION 1. Scope. — This Rule shall apply to appeals from judgments or final orders of the Court of Tax Appeals and from awards, judgments, final orders or resolutions of or authorized by any quasi-judicial agency in the exercise of its quasi-judicial functions. xxx
It is clear that the Court of Tax Appeals En Banc will only entertain petitioner's appeal if the assailed judgment is final. People v. Escobar explained the concept of final judgments and distinguished it from interlocutory orders:
A final judgment "leaves nothing else to be done" because the period to appeal has expired or the highest tribunal has already ruled on the case. In contrast, an order is considered interlocutory if, between the beginning and the termination of a case, the court decides on a point or matter that is not yet a final judgment on the entire controversy.
A thorough discussion on the difference between a final judgment and an interlocutory order is provided in Santos v. People, et al. The Court distinguishes final judgments and orders from interlocutory orders in this wise:
Section 2, Rule 41 of the Revised Rules of Court provides that "(o)nly final judgments or orders shall be subject to appeal." Interlocutory or incidental judgments or orders do not stay the progress of an action nor are they subject of appeal "until final judgment or order is rendered for one party or the other."
The test to determine whether an order or judgment is interlocutory or final is this: "Does it leave something to be done in the trial court with respect to the merits of the case? If it does, it is interlocutory; if it does not, it is final."
A court order is final in character if it puts an end to the particular matter resolved or settles definitely the matter therein disposed of, such that no further questions can come before the court except the execution of the order. The term "final" judgment or order signifies a judgment or an order which disposes of the cause as to all the parties, reserving no further questions or directions for future determination. The order or judgment may validly refer to the entire controversy or to some definite and separate branch thereof." 
In the absence of a statutory definition, a final judgment, order or decree has been held to be xxx one that finally disposes of, adjudicates, or determines the rights, or some right or rights of the parties, either on the entire controversy or on some definite and separate branch thereof, and which concludes them until it is reversed or set aside." The central point to consider is, therefore, the effects of the order on the rights of the parties. 
A court order, on the other hand, is merely interlocutory in character if it is provisional and leaves substantial proceeding to be had in connection with its subject. The word "interlocutory" refers to "something intervening between the commencement and the end of a suit which decides some point or matter but is not a final decision of the whole controversy."
In other words, after a final order or judgment, the court should have nothing more to do in respect of the relative rights of the parties to the case. Conversely, an order that does not finally dispose of the case and does not end the Court's task of adjudicating the parties' contentions in determining their rights and liabilities as regards each other, but obviously indicates that other things remain to be done by the Court, is interlocutory."Matute v. Court of Appeals explained why an interlocutory order cannot be the made the subject of appeal:
It is settled that an "interlocutory order or decree made in the progress of a case is always under the control of the court until the final decision of the suit, and may be modified or rescinded upon sufficient grounds shown at any time before final judgment xxx." 
Of similar import is the ruling of the Court declaring that "it is rudimentary that such (interlocutory) orders are subject to change in the discretion of the court."
Moreover, one of the inherent powers of the court is "To amend and control its process and orders so as to make them conformable to law and justice." In the language of Chief Justice Moran, paraphrasing the ruling in Veluz vs. Justice of the Peace of Sariaya, "since judges are human, susceptible to. mistakes, and are bound to administer justice in accordance with law, they are given the inherent power of amending their orders or judgments so as to make them conformable to law and justice, and they can do so before they lose their jurisdiction of the case, that is before the time to appeal has expired and no appeal has been perfected." 
And in the abovecited Veluz case, the Court held that "If the trial court should discover or be convinced that it had committed an error in its judgment, or had done an injustice, before the same has become final, it may, upon its own motion or upon a motion of the parties, correct such error in order to do justice between the parties. xxx 
It would seem to be the very height of absurdity to prohibit a trial judge from correcting an error, mistake, or injustice which is called to his attention before he has lost control of his judgment."
Further, the High Court held in Santos that interlocutory orders are barred from being appealed to avoid multiplicity of appeals:
Another recognized reason of the law in permitting appeal only from a final order or judgment, and not from an interlocutory or incidental one, is to avoid multiplicity of appeals in a single action, which must necessarily suspend the hearing and decision on the merits of the case during the pendency of the appeal. If such appeal were allowed, the trial on the merits of the case would necessarily be delayed for a considerable length of time, and compel the adverse party to incur unnecessary expenses, for one of the parties may interpose as many appeals as incidental questions may be raised by him, and interlocutory orders rendered or issued by the lower court.
In the case of CIR v. Omya Chemical (G.R. No. 237079. November 07, 2018), the main issue before the Court of Tax Appeals Second Division is the liability of respondent on its alleged deficiency taxes. When it issued the assailed Resolutions, it only dealt with the issue of prescription. Upon finding that petitioner's assessment of respondent's deficiency income tax, value-added tax, and expanded withholding tax for 2010 was void, it set the case for trial on the other deficiency tax assessments. Clearly, the Court of Tax Appeals did not "make a final disposition of the merits of the main controversy or cause of action."

It has yet to determine respondent's liability on its deficiency final withholding tax, documentary stamp tax, and final tax withholding. Thus, no other conclusion can be reached than that the August 30, 2016 and January 12, 2017 Resolutions of the Court of Tax Appeals Second Division are interlocutory orders, which cannot be appealed.

Moreover, allowing the appeal of the interlocutory orders before the Court of Tax Appeals En Banc may result to multiple appeals, if either party subsequently elevates the judgment of the Court of Tax Appeals Second Division on the remaining tax deficiencies. In prosecuting cases, the Supreme Court reminds litigants of its ruling in E.I. Dupont De Nemours and Co. v. Director Francisco, et al.:
Judicial economy, or the goal to have cases prosecuted with the least cost to the parties, requires that unnecessary or frivolous reviews of orders by the trial court, which facilitate the resolution of the main merits of the case, be reviewed together with the main merits of the case. After all, it would be more efficient for an appellate court to review a case in its entire context when the case is finally disposed.

ADDITIONAL READINGS:

[1] The Tax Court & its expanded jurisdiction - Project Jurisprudence.
[2] An Act Creating the Court of Tax Appeals (1954).
[3] Republic Act No. 9282 (2004).
[4] Republic Act No. 9282 (2004), sec. 11.
[65] G.R. No. 214300, July 26, 2017, 833 SCRA 180 [Per J. Leonen, Second Division].
[67] 585 Phil. 337 (2008) [Per J. Chico-Nazario, Third Division].
[69] No. L-26751, No. L-26085, and No. L-26106, January 31, 1969, 26 SCRA 768 [Per J. Castro, En Banc].
[71] Santos v. People, et al, 585 Phil. 337, 352 (2008) [Per J. Chico-Nazario, Third Division].
[72] E.I. Dupont De Nemours and Co. v. Director Francisco, et al, 794 Phil. 97, 113 (2016) [Per J. Leonen, Second Division].
[73] 794 Phil. 97 (2016) [Per J. Leonen, Second Division].