((a)) If any provision of this title requires the payment of interest on a tax claim or on an administrative expense tax, or the payment of interest to enable a creditor to receive the present value of the allowed amount of a tax claim, the rate of interest shall be the rate determined under applicable nonbankruptcy law.

((b)) In the case of taxes paid under a confirmed plan under this title, the rate of interest shall be determined as of the calendar month in which the plan is confirmed.