In the UK (and probably the rest of the EU) its a matter of law that prices for goods and most services are displayed including VAT and other taxes/charges. For example in the case of goods this currently set out in the Price Marking Order 2004 (SI 102, 2004) which is delegated a delegated power under s4(3) Prices Act 1974.

There are some exceptions, eg for B2B transactions and certain kinds of service, eg airtravel. But you still can't be misleading.

The above and other provisions have driven the expectation amongst consumers that the price you see is the price you pay. Other bodies (such as the Advertising Standards Authority) have quasi-judicial powers and generally regard it as misleading if the fully-inclusive price isn't shown to a consumer even if legally the supplier is entitled to do so.

As a consumer I find it much simpler if prices shown are fully inclusive. However I can't help thinking that if UK consumers were more aware of the amount of indirect tax they were paying at the point they pay it, they'd hold governments more accountable for the expenditure.