(1) The department is not required to accept fractional payments of the installments on certificate of purchase on account of the complications arising from the division of payments.
(2) The purchaser may make payment of one or more installments before the same becomes due, but unless such payments are made at least 6 months before the installments become due, no reduction may be made in the interest payments. If installments on principal and interest are paid more than 6 months prior to the due date, the interest from the date of such payment shall be figured upon the balance of the principal unpaid after the advance payment has been made up to the date on which it comes due.
(3) If for any reason any installment is not paid when due, the total of that installment, including payment on the principal and payment on interest, shall draw penalty interest at the rate of 6% per annum from the date due until the date actually paid.
(4) Payment may be made in full at any time before maturity by paying the balance on the principal and interest accrued up to the date of such payment.