For the purposes of this subchapter, all retail sales are consummated at the place of business of the retailer unless the tangible personal property sold is delivered by the retailer or his agent to an out-of-state destination or to a common carrier for delivery to an out-of-state destination. The gross receipts from such sales shall include delivery charges, when such charges are subject to the state sales and use tax, regardless of the place to which delivery is made. In the event a retailer has no permanent place of business in the state or has more than one place of business, the place or places at which the retail sales are consummated shall be determined under rules and regulations to be prescribed and adopted by the State Board of Equalization.
(`67 Code, § 6-2-7)