I released an extension that adapts the OXID shop to North American standards (including support for such things as taxes & addresses). It’s more than just a module because changes were necessary to several template files. As a result, a custom theme must be used, but this ‘theme’ is really just the Azure them with necessary changes made.
For more details see the README file.
Available here: https://projects.oxidforge.org/projects/v6c-nashop/
I posted a few live examples using the extension here: http://www.oxid-esales.com/forum/showthread.php?t=13597
Next up, a GPL PayPal module…