The registrar of motor vehicles shall:
(3) require recomputation of the percentage of intercity buses of any owner or operator at any time the registrar has reason to believe that an insufficient number of such intercity buses of such owner or operator are registered in Minnesota. If as a result of any such recomputation, the registrar of motor vehicles determines that additional intercity buses should be registered in Minnesota, the registrar shall require the owner or operator thereof to so register such additional buses and pay the taxes thereon in accordance with the standards required by this section. All intercity buses registered under the terms of this provision shall be registered for a full calendar year. All taxes computed on the percentage of intercity buses to be registered in the state of Minnesota shall likewise be computed on the basis of a full calendar year. If additional taxes are required to be paid by an owner or operator of intercity buses under this provision, such owner or operator shall also pay interest at the rate of six percent per annum on the amount so paid with interest computed from January 1st of the calendar year in which the taxes are due to the date of payment.