S.C. Code § 9-1-1180
The deductions authorized hereunder from the earnable compensation of teachers, the payments by employers of teachers of the required percentages of earnable compensation and all retirement allowances or other benefits herein provided shall be calculated upon the full earnable compensation of teachers from public funds derived from any source, and all employers' contributions for teachers shall be paid by the State. Provided, further, that all employers' contributions for employees of the various county technical training schools shall be paid by the State, effective July 1, 1962.
Payments for unused sick leave, single special payments at retirement, bonus and incentive-type payments, or any other payments not considered a part of the regular salary base are not compensation for which contributions are deductible. Contributions are deductible on pay for unused annual leave.
S.C. Code § 9-1-1180