Display Total including the Sales Tax:

I cannot find a spec field to do this. (I am using the field "Total Including Tax", but I am not getting the Tax!)

Note that we are entering the P/O initially with all Items back ordered – we obviously are not filling in the Received field at this time.

Example of what is happening:
Subtotal: 553.50
HST/GST: 71.96
Total: 553.50

The Total is wrong. How do we get this to display the correct amount (including the tax)?