Tax / GST Calculations

[Guest]

Hi,

I'm wanting to change the way the tax calculation works to be relevant for NZ and Australia.

Here the prices of product and freight are displayed as GST (Tax) inclusive but a tax calculation is usefull for the purchaser to know the GST content.

Where would I find the code to do this.

Say the tax rate is 12.5%, current method is product and freight cost $100 x 0.125 = final sell price = $112.50

Change this to;

Tax rate is 12.5%, product and shipping cost is $100 (which is tax / GST inclusive)

Calculation becomes, 100-(100/1.125) = $11.11

Tax ammount displayed as, GST Ammount = $11.11

Which pages of code would I need to edit to achieve something like this?

Aaron