Wrong Tax Calculation

Dear:

In my website, the tax's price is calculated based on the shipping price but not product's price, for example, if the product's price is $8, shipping price is $10 and tax price is 10%, then I will get a tax with the price $1($10 * 10%).

I have no idea about the reason because at first I know the calculation's result is right(I mean the result is based on product's price).

But now the result is based on shipping's price.

Would you please do me a favor to show me what is my fault?

This puzzles me so much!

Thank you a lot!

This sounds like there is an issue with the goods being marked as taxable/non-taxable

I am sorry but I don't understand.
Because in my store, products price seems to be excluded when calculating tax. Thus, my tax result is nothing to do with products price, only related with shipping price.
And I tried to remove the Group Discount Module, but nothing changed.