Sales tax is not recalculating on a Sales Order after the item quantities have been edited?

Client is using GP 2015. They sometimes need to edit a Sales Order item quantity prior to transferring the order to an Invoice. They have noticed that after some of the item quantity changes that the GP Sales Tax is still calculating upon the original Order total rather than the revised Order total.

Is there a setting that is missing in the Sales Tax setup that would help capture these changes?

Any suggestions?

Thanks

ML Suggs