27 C.F.R. § 31.171
A wholesale dealer may file the records of receipt and disposition required by §§ 31.155 and 31.156 in accordance with the wholesaler's regular accounting and recordkeeping systems. The required records must include the dealer's own file copies of the receiving or shipping invoices and must be filed according to the following rules:
(c) Supporting documents for receipts and dispositions, such as delivery receipts and bills of lading, also may be filed in accordance with the wholesaler's regular accounting and recordkeeping practices.
(26 U.S.C. 5121, 5122, 5123)