As a rule, the stated prices for most products and services should include all relevant sales tax charges. Naturally such prices cannot be stated on advertisements that are distributed to different political jurisdiction with different tax rates, but it could easily be done with the goods and serviced sold by physical stores.
Furthermore, this principle should be applied as widely as possible. Shipping charges, if they are the same throughout the advertised area, should be included as part of the advertised price of the product. In essence, a customer should not have to add up a whole bunch of other numbers (such as taxes, shipping charges, mandatory fees, etc.) in order to arrive at the ‘true’ price of a product. Though it is naturally impossible to completely achieve this due to differing tax rates and other factors, prices should be as close to ‘true’ as possible. As much as possible, customers should be able to give the seller the amount stated on the price, and be able to walk away with the product.
The receipts would, of course, breakdown exactly what taxes and other charges are included in the final price.