Tenn. Code Ann. § 67-6-535

The department may enter into a reciprocal agreement with the comparable department of another state to furnish records concerning purchases made by citizens of the other state from a dealer in this state where the dealer collects neither a sales nor a use tax on the sales; provided, however, that the other state agrees to furnish the same records to this state and each sale is in excess of five hundred dollars ($500). All dealers in this state making sales to purchasers in another state where no sales or use tax is collected shall furnish the department copies of all the invoices or suitable substitutes for sales in excess of five hundred dollars ($500) upon request of the department; provided, however, that the department notifies the dealers of the existence of a reciprocal agreement.