For the purpose of compensating a dealer holding a certificate of registration under § 58.1-613 for accounting for and remitting the tax levied by this chapter, such dealer shall be allowed the following percentages of the first three percent of the tax levied by §§ 58.1-603 and 58.1-604 and accounted for in the form of a deduction in submitting his return and paying the amount due by him if the amount due was not delinquent at the time of payment. The discount allowed by this section shall be computed according to the schedule provided, regardless of the number of certificates of registration held by a dealer.