You can choose to have Accounts Payable automatically calculate and distribute taxes that should be listed separately on the invoice.
To calculate excluded taxes automatically:
Accounts Payable > A/P Transactions > Invoice Entry.
Select an invoice, or enter a new one, as usual.
Before proceeding to the next step, make sure that on the Document tab, you have:
On the Taxes tab:
Click Distribute Taxes.
Note: Because detail taxes are calculated automatically, you cannot change the allocated tax directly for detail lines on the Document tab. However, you can change the tax class or Tax Included setting for an individual line, as described in step 3.