The AMA is only concerned with the image of medicine. A more practical matter is the government's regulations.
http://www.vitaminshoppe.com/content/en/support/help/sales_tax.jspThis website lists the exclusions for sales tax based on your state regulations. Most states tax supplements. Not sure how that applies to your practice.
Bummer if your local government determines you to be a revenue source and comes looking for the overdue sales taxes for the last 3 years, and the money is spent or the records are sparse.