How to tax calculate when i am adding a product?

Hi,

I add a field "GST Rate TAX" in Product Catalog entity, suppose I set a GST Rate TAX: 5% and my product rate is Rs.1500.

Now I am want when I am adding a product in opportunity and tax would be calculate automatic and i think this task should be completed by Plugins.

Please give me suggestion how to solve.

Thanks in advance.