Montana Gross Receipts Tax

When we are awarded a contract (over $6,000) being paid for with Montana Public Funds we are required to pay 1% of our gross earnings to the state. This is usually just withheld from us by the project owner and they send the payment to the state for us and in turn, we withhold 1% from our subcontractors when we send them payment on the same project. 

We have been utilizing Sage's retention feature for the actual retention, but the gross receipts tax is calculated after that, so we just manually enter the actual amount we are paid and the amount we pay our subs .

This leaves 1% of our contract with the owner showing as a balance due in receivables and a 1% balance due to all our subcontractors in our payables even though everything has been billed and paid. 

What is the best way to clear these amounts off the A/R and A/P without altering the contract amounts?