If you don't have the manual for your register you can download one here:
http://www.sharpusa.com/CustomerSupport/ProductDownloads.aspx
Take a look under "Getting Started" for the section titled "Tax Rate Programming". This will tell you how to set the tax rate(s) that is being used. By default, Depts. 1 - 4 are taxable by rate 1, Depts. 5 - 8 are not taxable. If you want to change this, consult "Department Status" under "Programming By Departments" in the Programming section of the manual.
Hope this helps ...
Steve, January 2010