Sub total issue in checkout

-- url of the page with the problem -- : site not yet live
-- HikaShop version -- : Current Business version
-- Joomla version -- : 3.2 Stable
-- PHP version -- :5.4.14
-- Browser(s) name and version -- : Firefox 25.0.1
-- Error-message(debug-mod must be tuned on) -- : Not an error message


Hi again, hope someone can advise what code I need to change/add and where, to help me fix the sub-total problem I am having as this is a law requirement for Australia, I need to have the subtotal show the correct amount.

Currently this is what shows in the cart and is emailed to the customer.

Sub total $18.00
GST $1.64
TOTAL plus GST $18.00

As you can see the Sub total is incorrect and should be $16.36

So I need it to show as:

Sub total $16.36
GST $1.64
TOTAL plus GST $18.00

Any advice and guidence again would be greatly appreciated,

Kind regards
Jennifer

Can someone please advise where or which view and what php code to change to do this... please... really need some guidence here

Cheers
Jennifer