A contract solicited by competitive sealed bids shall be awarded with reasonable promptness by written notice to the lowest responsible bidder. Contracts solicited by competitive sealed bids shall require that the bid amount exclude the applicable state gross receipts tax or applicable local option tax but that the contracting agency shall be required to pay the applicable tax including any increase in the applicable tax becoming effective after the date the contract is entered into. The applicable gross receipts tax or applicable local option tax shall be shown as a separate amount on each billing or request for payment made under the contract.