I posted before, but realised I didn't provide enough information or link the correct plug-in, apologies.
I was using Market Press Lite and needed the tax inclusive pricing for Australian legal compliance, After seeing the feature was introduced in MarketPress 2.2 and upgrading I'm still having some problems which are preventing me going live with my site.
1. When going to checkout, the price of the products is displayed correctly, but the total price is pre-tax.
2. The product amount(s) on PayPal Express is still pre-tax.
3. The shipping amount is not tax-inclusive, resulting in the tax being applied twice.
Essentially, the only improvement I can see is that the displayed prices are tax-inclusive, but when it gets to the payment stage it's still not showing everything as tax-inclusive, which is absolutely critical for Australian law and many other countries, judging by the posts here.