Prices across regions with different tax

Where I am from all prices advertise must be the price you pay. What you see is what you pay. This means that taxes, fees and anything else must be included in the advertised price. This is regardless of the price is advertised in a physical store, online or in a commercial somewhere.

I have seen (especially) Americans argue that the business owner should only care about their own price and not what tax the consumer must pay on top of the "base price" and therefore should be able to advertise the price without tax. To me this seems odd because no matter what the business owner is the one who must calculate the tax and also pay it to the relevant authorities afterwards. From a consumer protection perspective it also makes sense that the advertised price is the one you must pay.

However, I can see one point where the prices without tax make sense. If a company want to market a product across several states in the US where the sales tax might differ it would be difficult to show the final price since the company does not necessarily know where the person resides / what tax is applied.

Therefore, is there anywhere in the world where a region with same currency, but different sale taxes require that the advertised price is the price the customer pays? And if so, how is it handled when companies uses the same advertisement across the entire region?

The Eurozone is an example of this. Ordinary VAT varies from 18% (Malta) to 25.5% (Finland). The more difficult issue is that treatment of certain items, like food and medicine, vary. France, for example has 4 reduced rates including zero that apply to these goods.

Basically, you have two options generally. One is to advertise different prices in different countries. In the Eurozone, this usually works because languages differ, so the advertisement can't be the same anyway.

The second option is for the manufacturer to absorb any difference in taxes, selling the good for different pre-tax prices in different regions. One could say that the manufacturer is pocketing the difference in lower-tax areas. This is a major reason why tax-exclusive prices are advertised in the US and Canada, often by law.

Related, Japan is inconsistent with how it's relatively young (1989) consumption tax is handled. Sometimes prices displayed in stores are tax-inclusive, other times both prices are displayed with the tax-exclusive price being more prominent. Prior to 2021, they could even show tax-exclusive prices.