S.C. Code Ann. § 12-36-2610 – When a sales or use tax return required by Section 12-36-2570 and Chapter 10 of Title 4 is filed and the taxes due on it are paid in full on or before the final due date, including any date to which the time for making the return and paying the tax has been extended pursuant to the provisions of Section 12-54-70, the taxpayer is allowed a discount as follows:

(1) on taxes shown to be due by the return of less than one hundred dollars, three percent;
(2) on taxes shown to be due by the return of one hundred dollars or more, two percent.
In no case is a discount allowed if the return, or the tax on it is received after the due date, pursuant to Section 12-36-2570, or after the expiration of any extension granted by the department. The discount permitted a taxpayer under this section may not exceed three thousand dollars during any one state fiscal year. However, for taxpayers filing electronically, the discount may not exceed three thousand one hundred dollars. A person making sales into this State who cannot be required to register for sales and use tax under applicable law but who nevertheless voluntarily registers to collect and remit use tax on items of tangible personal property sold to customers in this State is entitled to a discount on returns filed as otherwise provided in this section not to exceed ten thousand dollars during any one state fiscal year.