After having Taxt Rate and Tax Class already, what you have to do is to add a Tax Rate to an existing Tax Class in OpenCart. In this tutorial I will show you how to do it step by step.
Step 1: Log into OpenCart Dashboard
Step 2: Go to System >> Localisation >> Taxes >> Tax Classes
Step 3: Click Edit in Tax Class that you want to add Tax Rate
Step 4: Click Add Rule choose Tax Rate and Based On
So if your customer purchases a product that is assigned to specific tax class and the address they enter matches the Geo Zone that assigned to the Tax Rate, the tax wwill be applied to this product immediatly. There are many OpenCart tutorial and information about news OpenCart themes of Kulerthemes will be released soon. Please stay tuned!