I'm running Zen Cart v1.3.8a and is able to setup the following by installing the
Dual Pricing - Wholesale Pricing v1.4.2 and
Customer Tax Exempt v1.12.
[*]retail prices shown to the general public.
[*]wholesale prices shown only to wholesale customers once they have logged-in.
[*]wholesale customers are exempt from paying provincial retail sales tax once they provide their tax exemption number.
Just installed both mods, extract and upload (replace) the attached customers.php to the admin folder. I have combined the codes from both mods.
You can then grant wholesale status and tax exempt status on admin->customers. (In my case, I entered "1" for Wholesale pricing level and "New York State Sales Tax" completely for Customer Tax Exempt.)
It's working fine for me

but keep in mind that use this AT YOUR OWN RISK!
