Yes the cart supports role based discounts, to setup role based discounts go to the BuyNow module settings under the discount section and check the box titled "Enable Order Level Discounts By Role." If you check this box it will enable order level discounts by role. Order level discounts by role only when a user is logged in and a member of the role you define. Order level discounts by role are applied to the order subtotal and can be configured as a discount percent or discount amount. To define order level discounts by role click the discounts button on the store admin menu and setup your discounts by role.