(1) Duty under this Chapter is to be assessed on the total amount of the hiring charges received in a month by the commercial hire business.
(2) The Commissioner may, however, by notice in writing approve a different basis of calculation of hiring charges if it appears to the Commissioner that duty payable on that basis will, over a period of time, approximate the duty payable in accordance with subsection (1). An amount calculated under any method so approved is taken for duty purposes, while the approval remains in force, to be the amount of hiring charges received. Such an approval may be revoked by the Commissioner at any time by notice in writing to the commercial hire business concerned.
(3) A registered commercial hire business can, with the Commissioner's written consent, change the basis (as between a receipts basis and an approved basis) from month to month but it cannot change the basis within a month.
(4) If consent is given under subsection (3), the Commissioner may assess or reassess the duty payable in any period prior to the change of basis to include any hiring charges that would not be accounted for, or to exclude any hiring charges that would be accounted for twice, because of the change of basis.