We are trying to implement SAP Note 2630754 - Tax not Sent in cXMLOrderRequest_Out to Ariba - SAP ONE Support Launchpad is it possible for EHP7 FOR SAP ERP 6.0? Because we are unable to see BAdi on our end? Thank you.
The note does not seem to be related to CIG. The note talks about cxml, but we are sending IDOC for PO out of SAP....
SO, I will confirm with the owner of the solution note once she is back from leave (a few days).
Meanwhile, you should take a look at this blog post that explains and provides some ABAP code on taxes in AN:
This is usually what our partners end up using to achieve tax on PO.