(a) Interest penalties payable on amounts due to a qualified small business concern under this article shall be paid to the business concern for the period beginning on the day after the required payment date and ending on the date on which payment on the amount due is made except no interest penalty shall be paid if payment for the complete delivered item of property or service concerned is made on or before the 15th calendar day after the required payment date.

(b) Interest shall be computed at the rate determined by the Secretary of Revenue for interest payments on overdue taxes or the refund of taxes as provided in sections 806 and 806.1¹ and any subsequent amendments to those sections.

(c) Interest may be paid by separate payment made to a qualified small business concern within thirty days of payment of the original invoice.

(d) Any amount of an interest penalty imposed because of a debt which remains unpaid at the end of any thirty-day period shall be added to the principal amount of the debt and thereafter interest penalties shall accrue on the added amount.