To override the manual sales tax, the order must be in Entered status. Place the mouse pointer over the word Tax in the grey summary box and a small message box appears “Click to override tax charges”. (You do not have to wait to see the message; you can simply click on the word Tax).

When you click on the word Tax, the “Manual Override Tax Charges” box appears. Click in the box to open the Edit Tax dialog box.

Enter the Tax amount and click Save in the dialog box.  The changes will be reflected in the grey summary box.  Do not click Save on the left-navigation bar because the tax charge formula will be applied and your changes will be overwritten.