In Bibb County, any supernumerary tax assessor-collector serving on August 1, 2016, shall be entitled to a three percent cost-of-living increase in compensation. The sum to cover the cost-of-living increase shall be deducted on a pro rata millage basis by the tax collecting official in the county from taxes collected and shall be paid to the supernumerary official in the same manner as the salary of the supernumerary official is paid pursuant to Section 40-6-3.