O.C.G.A. § 48-2-10

The commissioner is authorized to negotiate and contract with the governing authority of any county or municipality for the purpose of arranging for the collection by the commissioner of any tax levied by the county or municipality when the tax is also levied and collected by the commissioner for the state. The agreement shall include a fee to be paid by the county or municipality to the commissioner in an amount which covers fully the cost of collection of the local portion of the tax by the commissioner. The commissioner shall transmit to the county or municipality all taxes so collected on behalf of the county or municipality on or before the date specified in the agreement, less the collection fee agreed upon.