Tennessee Code Title 5. Counties § 5-21-115

(b)(1) Before any obligation against the county shall be paid or any disbursement warrant or voucher issued, a detailed invoice, receivable copy of the purchase order, or such document indicating receipt of merchandise or service should be approved by the head of an office, department or agency for which the obligation was made and be filed with the director.

(2) The director shall establish a system for making a careful preaudit of such invoice, purchase order, or other documents, including a comparison with any encumbrance document previously posted or filed authorizing such obligation, and shall approve for payment only such items as appear to be correct, properly authorized, and not exceeding the otherwise unencumbered balance of the allotments or appropriations against which they are chargeable.

(3) Disbursement warrants shall be promptly prepared for all such approved obligations by the director, signed in accordance with § 5-21-116 and mailed or delivered to the payees thereof.