If a taxable item is exempted from the taxes imposed by this chapter, the sale, storage, use or other consumption of the item is not subject to the sales tax imposed by § 151.051 of this code or the use tax imposed by § 151.101 of this code if the item meets the qualifications for exemption as provided in this subchapter; and when an item is exempted from the taxes imposed by this chapter the receipts from its sale are excluded from the computation of the taxes.