@cell113 sorry for 'promoting' your comment as a post, but this is the usual explanation I heard about this, and I need to show you USians something.
I just took this picture from my kitchen:
That's some pasta and couscous, bought at one of the largest supermarket chains in Europe. I want to point your attention to the text in the bag and box. The pasta bag is both in Spanish and Portuguese. The box, Spanish and french.
Due to shared distribution chains, it's extremely common for any single product to be sold in different countries of the EU. You could get that pasta bag in Porto or in Madrid. You could get the couscous in either Valencia or Marseille. The taxes in every one of those three countries are extremely different (for example, France have a 5.5% VAT on food, Portugal 6%, Spain 10%), the distribution chain is the same, the supermarket selling them is the same. The end price is different in every case. And yet, every store just labels every product with their local after-taxes price.