ed810 not pulling tax

we are currently 8.03 sitting on 9.0lsf and use Ghx as our provider for EDI. We currently became a tax company and we seem to have a problem at month end with out of balance for AP due to tax. WHen you look the tax is not be added to the invoice and we run the ap126 which matches and were done.
Has anyone set up edi for tax ?  I'm begining to think that this is the problem. If not and anyone has a great suggestion on how to fix this I would greatly appreciate your help.
The only one we have an isue with is our edi vendor for 810s. all the rest of our vendors the tax is being addede as an aoc code for sales tax and then entered on the ap20 screen. The only ed810s that work with tax are those we have to fix for other issues and we add the tax.