add total ex to the check payment page

[bluesky2008]

on the check payment page, my current billing is

Sub-total Inc: $11.00
Shipping cost: $5.00
Tax: $1.00
Total: $16.00

i want to add the price ex, then make it as

Sub-total Ex: $10.00
Sub-total Inc: $11.00
Shipping cost: $5.00
Tax: $1.00
Total: $16.00

what do i make it done? thanks