For members with a partial month of service at the time of retirement, creditable service shall be rounded to the nearest one-half (1/2) month of service. For this purpose, thirty (30) days shall constitute a full month of service and fifteen (15) days shall constitute a half month of service.
Ga. Comp. R. & Regs. R. 513-8-1-.02
O.C.G.A. Section 47-8-3.