Example:
I have a product including price is RS 1750 (inr) and tax rate is 5.5%.
And my shopping CART is showing like this
SUBTOTAL RS 1,658.77
TAX RS 91.23
GRAND TOTAL RS 1,750.00
But 5.5% of 1750 is 96.25
So what is the wrong?
you can edit some setting as you need in your cart
System > Configuration > Sales > Tax > Shopping Cart Display Settings
Display Subtotal Store View Determines whether the shopping cart subtotal is shown with tax, without tax, or both.
Excluding Tax: Shopping cart subtotal does not include tax.
Including Tax: Shopping cart subtotal includes tax.
Including and Excluding Tax: Shopping cart subtotal is displayed with and without tax.
you can also refer doc here
hope this will sure help you
(1658.77*5.5)/100=91.23
1658.77+91.23=1750