It's fairly regular for us to have sales where some pieces on an invoice are being shipped, and some are being taken out the door, which are different tax/shipping situations per piece and the one option of tax for the whole sale, or shipping for the whole sale isn't cutting it to make this an accurate invoice for our clients, as well as our accounting on the back end.

I see the current suggestion for this when it comes to shipping, but tax is the same way for us as well.