S.C. Code Ann. § 56-11-430

Every motor carrier subject to the tax imposed by this chapter shall, on or before the last day of April, July, October, and January submit to the Department of Motor Vehicles the reports of its operations during the quarter of the year ending the last day of the preceding month as the department requires. Nothing in this section may be construed to eliminate the requirement as to registration and identification markers otherwise provided by this chapter.