The exemption provided for in § 47-2005(19) shall apply to sales made on or after January 1, 1978. Any tax collected by the District of Columbia from a vendor on such exempt sales and any reimbursements collected by a vendor from purchasers on such exempt sales shall be refunded in accordance with § 47-2020; provided, that no interest shall be allowed or paid on any amount refunded pursuant to this section.
D.C. Code § 47-2006