All invoices shall be delivered promptly to the Department of Finance which shall prepare a voucher and audit it to see that it is complete and correct and that the order was legally made. The outstanding encumbrances shall be credited and the cash balance debited in each case and a check written in payment. Any adjustments due to shortages in deliveries, reductions in price or discounts taken shall be made when the entries affecting encumbered balances are made. Checks shall be signed by the Director of Finance and by the City Manager and shall be delivered promptly to the claimants.