This Zen Cart Easy Help tutorial explains how you can troubleshoot problems with your taxes calculating incorrectly. If you are not sure that you have configured your taxes correctly, take a look at our tutorial about how to properly configure US single rate taxes. If you have followed all the instructions, but your taxes are still not calculating properly, there are a few settings you can check to ensure that they are all correctly configured. To do this, you will need to open and log into your zen cart admin area.
First, go to admin->Configuration->My Store, and make sure that all of these settings are right: Country/Zone, Basis of Product Tax, Basis of Shipping Tax, Display Prices With Tax, Display Prices With Tax-Admin.
If all of these settings are correct, move on to Admin->Locations/Taxes->Zones Definitions, and make sure your zones have been properly configured. If they are, check within each zone definition by clicking on the ‘details’ button for each zone. Here, make sure that the correct country/zone combinations have been selected.
You should also check Admin->Locations/Taxes->Tax Classes to ensure that your taxes classes have all been created and Admin->Locations/Taxes->Tax Rates to make sure your rates are all properly defined. Keep in mind that if you change anything during the course of your troubleshooting, you should place an order on your store to see if the taxes have started calculating correctly before making any more changes.
You can also check to see if the tax class associated with your products is correct in Admin->Catalog->Categories/Products. Here, you will need to click on your products to check/edit them. Also take a look in Admin->Modules->Shipping to make sure your shipping modules are configured with the right tax class.