Final price in cart page counting tax before applying coupon code

Final Price : 100, so 3 % tax on this 100 = > 103 should be final price, fine.

Now apply coupon code to get 50 % discount , so tax on 50 : 1.5 {3 % }

Issue :

Now Final price is 53 [ 50 + 3 ], it is not calculating tax after applying coupon code.

Result should be 51.5 [ 50 + 1.5 ]