Notwithstanding any other provision of law, the Commissioner may from time to time make regulations to provide that "taxable cost" shall not reflect a diminution for trade-in arising from a purchase of a motor vehicle in a state which does not allow a deduction for trade-in in the computation of the "taxable cost" or similar tax base in the computation of taxes imposed by a motor vehicle sales and use tax in that state. (Added 1967, No. 116, § 6, eff. April 17, 1967.)