Could you provide more info? Is this in the AP window, in the the Tax code field?

No this is the field for HST on the Job Cost (6-3) for Time & Materials.

If you have admin privileges, you have the option to put a check mark on override billing amount which then enables subject to GST/HST/PST. Once its enabled you have the option to put a check mark (1 or 0 for off). I hope that helps.

That helps but what I trying to determine is why I have to do this for some transactions and not for other transactions.  

This could be a couple things; T&M setup 3-10-1 or whether the items should be charged tax based on your jurisdiction or provincial rules.

This could be a couple things; T&M setup 3-10-1 or whether the items should be charged tax based on your jurisdiction or provincial rules.