If you are in Europe, then typically you will want to enter prices on your web site inclusive of tax. Stores based in the US, or European stores that deal primarily with business customers, will normally want to enter prices exclusive of tax.

This is controlled by the general.tax.pricesinctax config setting which should be set to 'y' for tax inclusive prices, and 'n' for ex-tax prices.

Note that for tax inclusive prices, tax is calculated 'per item' rather than per row of the basket. As such, a rounded 'ex tax' price can be calculated. But for ex-tax pricing, tax is applied to each row of the basket. Consequently, it is not possible to show a rounded inc-tax price for individual items, because this would in many cases not quite tally with the actual tax on the order (due to the different rounding used, per-item and per-row) and would be likely to confuse customers or lead to complaints that the site has added up the tax wrongly.  Instead a percentage figure is shown where necessary.