If the first payment is not paid when due, the entire tax becomes delinquent and subject to a penalty of 10 percent of the entire tax and interest shall accrue on the unpaid principal balance, excluding the penalty, at the rate of 12 percent per year. If the first payment is paid when due but the second payment is not paid when due, the unpaid balance of the tax becomes delinquent and subject to a penalty of 10 percent of the unpaid balance, and interest shall accrue on the unpaid principal balance, excluding the penalty, at the rate of 12 percent per year. Partial payments shall be applied first to accrued penalties, then to interest, then to principal. Notwithstanding the acceptance of partial payment, the unpaid balance remains delinquent and the lien therefore enforceable in accordance with law. For the purposes of this section, a payment is paid when due only if it is physically received in the borough finance office by the due date or is postmarked by the United States Postal Service, on or before the due date. Payments received after the due date that bear a postmark generated by a metered machine that is not in the possession and control of the United States Postal Service shall be deemed delinquent. [Ord. FY2015-10 §10, 2015; Ord. 99-02 §2, 1999; Ord. 93-36 §2, 1993; Ord. 86-25-O(A) ; Ord. 82-33-O, 1982; Ord. 80-22-O §1, 1980. Formerly §3.20.090].