It is hereby declared to be the intent of the Legislature that one rate of excise tax shall be applicable to all quantities of gasoline or special fuel in this state on and after the effective date of any increase in the rate of such tax. Any gasoline or special fuel on hand or in inventory on the effective date of any rate increase is hereby deemed to have been purchased or received on such date.

Every distributor, retail dealer or importer subject to the tax imposed under this article, who, on the effective date of any rate increase, has on hand or in inventory any gasoline or special fuel upon which tax or any portion thereof has been previously accrued or paid, shall, within thirty days after such effective date, take a physical inventory and file a report thereof with the commissioner, in the form prescribed by him and shall pay to the commissioner at the time of filing such report any additional tax due under an increased rate.