Service tax on incentive received

A & Co. is a authorised dealer of car & it purchase vehicle from its supplier and sale to its customer. In addition to the regular profit on sale of vehicle, A & co. also received incentive on monthly, quartely & yearly basis from its supplier which depends on achievement of sales target as decided and intimated by its supplier from time to time. My question is whether such incentive received is taxable under service tax act and under which category.