Not a direct solution, but some potential pointers/ideas.
Look into the tax helper class.
There is a method there
->getPrice that may work for you.
There are a lot of other interesting methods to look into.
Also have a peek at
Mage_Catalog_Block_Product_View_Type_Configurable::getJsonConfig in there you will see some tax related logic that may also be of use/give you some idea of what can be done.
Look towards teh middle of the method, where the code begins with
$taxCalculation = Mage::getSingleton('tax/calculation');
Also some potential help here:
see the code as follows in that routine:
$price = $taxHelper->getPrice($product, $product->getPrice());
$regularPrice = $taxHelper->getPrice($product, $product->getPrice(), $simplePricesTax);
$finalPrice = $taxHelper->getPrice($product, $product->getFinalPrice());
$finalPriceInclTax = $taxHelper->getPrice($product, $product->getFinalPrice(), true);