By default the POS uses the store location for the tax, so you need to have a tax rate set up which matches your Base Location.
The most common problem is that the store location only goes to a state level, e.g.: Alabama, but the tax rates can go down to a City or Postcode level, e.g.: Huntsville or 35805. You need to make sure you have a tax rate set for Alabama as a state and then you should see tax in the POS.