Ecommerce Plugin with Quantity Specific Pricing Options

I am trying to find a wordpress plugin for eCommerce that will allow for advanced pricing options. Specifically, we have products that come in cartons of 4. We have a carton quantity sell price and a less than carton quantity sell price.

for example, if they purchase 4 the price each will be 15.00. If they less than 4, the price will be $16.00 each. This also needs to apply to if they buy 5, 4 of them will be 50.00 and one will be 16.00.

Does anyone know of a good shopping cart plugin with quantity specific pricing options?

Thanks