Oversecured creditor was entitled to postpetition interest under § 506(b), but penalty portion of Government’s tax claim was not part of claim entitled to interest. Applying rationale of Bondholder Committee v. Williamson County (In re Brentwood Outpatient, LTD), 43 F.3d 256 (6th Cir. Dec. 13, 1994) (Merritt, Milburn, Siler), although § 506(b) was amended by BAPCPA to add state statute as basis for oversecured creditor’s recovery of interest on non-consensual liens, conclusion in Brentwood that § 506(b) did not include penalties was still valid. “Penalty” was not within § 506(b) “fees, costs or charges.”