In Biernacki v. Redevelopment Authority of the City of Wilkes-Barre, 32 Pa. Commw. 537, 379 A.2d 1366 (Pa. Cmwlth. 1977), the Court vacated a trial court's order because of the failure to join an indispensable party; we also dismissed the petition below without prejudice to the appellee's right to institute a new action wherein all indispensable parties could be joined. Failure to join an indispensable party to a lawsuit deprives the court of subject matter jurisdiction. Polydyne, Inc. v. City of Phila. 795 A.2d 495 (Pa. Cmwlth. 2002). Whether a court lacks jurisdiction due to the failure to join an indispensable party may be raised at any time or sua sponte. Id. A party is deemed to be indispensable when his or her rights are so connected with the claims of the litigants that no decree can be made without impairing those rights. Id. Significantly, this Court has held that a successful bidder at a tax sale is not a party, as a matter of course, to objections to a confirmation nisi. In re Consol. Return of Real Estate Tax Sale Held September 10, 2003 by Tax Claim Bureau of County of Lackawanna, 859 A.2d 15 (Pa. Cmwlth. 2004) (Sposito Appeal). In that case, the Court recognized some trial courts require a successful bidder at an upset sale to intervene in order to become a party to a hearing on objections to an upset sale. Id. at 18. Because a trial court is not required to follow the Pennsylvania Rules of Civil Procedure in tax sale proceedings, "it is within the discretion of the trial court to specify the procedure by which the purchaser may challenge the objections and exceptions to a tax sale." In re Sale of Real Property Situate in Paint Township, Somerset County, 865 A.2d 1009, 1015, n.11 (Pa. Cmwlth. 2005) (Baumgardner Appeal). Moreover, in Baumgardner Appeal, we recognized that the "filing of exceptions overcomes the presumption of regularity in the tax sale" and thus the burden is on the tax claim bureau to demonstrate strict compliance with the notice provisions of the Tax Sale Law. Id. at 1015. Although these challenges are often defended by both the tax claim bureau and the purchaser, the purchaser must seek to intervene in order to participate. Id.