Hi,
The price with options is displayed dynamically by an ajax routine which just send the calculated price and gets back the display.
It uses for that the file "option_price" for that.
However, that view file only knows the amount to display, no other information.
If you have only one tax rate and it always apply, then it will be easy to modify the option_price view file.
Otherwise, you'll have to also modify the "option" view file to adapt the javascript code calculating the total in order to send more information to the option_price view file in orde to be able to display both amounts.