Imagine you've got a return with a line for $500 and a tax adjustment of $150, what you'll see on screen is a total of $650. Which will be correct. What you'll see in the database is a 500 in the coitem table and a -150 in the cmheadtax table. This is the desired functionality of the data model and the application.

So I have to multiply the taxes by -1. I don't like the idea of using abs() because, for all I know, you might have a negative negative tax somehow. If coitem says 500 and cmheadtax says 150, then I would presumably want the app to show $350.