Well if you look at my site http://www.idastroke.co.uk you will see that the prices for the items on the home page are displayed excluding VAT. If however you look at the category pages you will see that the prices are displayed including VAT.
So taking one item as an example. Its price is £13.33 (excl VAT) and should be displayed as £16.00 (including VAT). It is displayed as £16.00 on all the product and category pages BUT is displayed as £13.33 on the slider on the home page.
Thus something in the theme is not picking up the correct price.