Ga. Code § 48-8-70
If a nine-digit ZIP Code designation is not available for a street address or if a seller or certified service provider is unable to determine the nine-digit ZIP Code designation applicable to a purchase after exercising due diligence to determine the designation, the seller or certified service provider may apply the rate for the five-digit ZIP Code area. For the purposes of this Code section, there is a rebuttable presumption that a seller or certified service provider has exercised due diligence if the seller has attempted to determine the nine-digit ZIP Code designation by utilizing software approved by the Streamlined Sales Tax Governing Board that makes this designation from the street address and the five-digit ZIP Code applicable to a purchase.
OCGA § 48-8-70