Need a Shopping cart that does discounts per vendor

We are a distributor that sells various items.  A contractor might get 20% off windows and 30% off doors.  We need the ability to assign these discounts per user or a role (in which the customer is assigned to) to receive this discount.

DotShoppingCart allows you to assign a role to a customer but it's an across the board discount over all the list price items but not broken down by vendor.

Is there a shopping cart that will allow us to do this?