This idea has been merged into another idea. To comment or vote on this idea, please visit MXM-I-188 Invoice/Order Level Tax.
Currently on Invoices/Contracts/Orders make you apply tax by the line item, which depending on how many line items you have it can be quite difficult and time consuming to add. It would be really nice to have what was available in MX4/5 where you can add tax once to the entire thing and it will apply to all of the line items.