Bills can be confusing to customers because of the regulations asking us to display the price incl. VAT to them and at the same time forcing us to declare the tax base.
For example when offering the customer a 20.00 Euros discount (using the uc_coupon module, discount type "Price") the order total preview show the amount before taxes which in Spain would be 17.24 Euros. My solution would be to have a table with three columns: "Price excl. VAT", "VAT", "Total" and four rows "Subtotal", "Shipping fee", "Coupon", "Total". Ok that's "Total" twice, maybe labeling could be better... This idea could be pushed even further: add an extra column to show the VAT rate (as when products with different tax rates are billed, then we need to declare the tax base subtotal for each rate).
Now I don't know how feasible this is with Ubercart 2, maybe the request needs redirection to the core?