OK, I love the idea but it seems it doesn’t work with European format prices. E.g. on Amazon.de, a product costs 42,87 €. That should be rounded to 42,90 but it’s instead “rounded up” to 4.290,00 € ! I suppose this is because the extension is look for a “.” thousands separator, but in Europe we use “,” instead.
E.g. ten thousand euro = 10.000,00 € (not 10,000.00 €)
EDIT: It's all of Amazon.de — not a specific page. Tried on Arc browser.