Totalling the cost of Service Catalogue Shopping Cart

Hi

Am I missing something obvious here or is there no functionality to add multiple items to the shopping cart and have it total the cost of all the items?

For example, I would like to add 3 computers of the same type by selecting the item, selecting the number required and adding it to the shopping cart and the shopping cart totals the cost of the 3 computers

Any advice appreciated

Thanks

Jason