Any retailer who purchases from the manufacturer at or at less than or at about the price normally and usually charged for purchases in wholesale quantities shall, in determining cost to the retailer, pursuant to § 37-10-5, add the cost of doing business by the wholesaler, as defined in §§ 37-10-9 and 37-10-10, to the basic cost of cigarettes to such retailer, as well as the cost of doing business by the retailer.
SDCL 37-10-7