Hi,
Turning the option "Show taxed prices" to "No tax" in Configuration > Main > Taxes is not enough ?
When you are talking about the cart, which cart, the module or the cart display page which can be reached via a menu or the user control panel ?
For the cart module, the view calling the "product / listing_price" one is "product / cart".
Else the view is "cart / showcart" and call the view "cart / listing_price".
And as you said, you can change the tax display option directly in the "listing_price" view.