(1) For the purpose of determining the amount of his liability for the tax imposed herein, each Class A distributor shall, not later than the twentieth day of the month next following the month in which this article becomes effective and not later than the twentieth day of each month thereafter, file with the commission a monthly report which shall include a statement of the number of gallons of lubricating oil sold by such Class A distributor within this state during the preceding calendar month and such other information as may be necessary for the proper administration of this article.

(2) At the time of filing each monthly report with the commission, each Class A distributor shall pay to the commission the full amount of the lubricating oil tax due from such Class A distributor for the preceding calendar month.

Reports and payments sent to the commission by mail must be postmarked by the due date in order to be considered timely filed, except when the due date falls on a weekend or holiday, in which case such reports and payments must be postmarked by the first working day following the due date in order to be considered timely filed.

The monthly report of the Class A distributor shall be prepared and filed with the commission on forms prescribed by the commission, or such Class A distributor may, with the approval of the commission, furnish the required information on machine-prepared schedules setting out such information as is prescribed on the forms furnished by the commission. Such monthly reports shall be signed by the Class A distributor in person or by his duly authorized agent and shall contain a declaration that the statements contained therein are true and are made under penalty of perjury.