I know how VAT works. If the government changes the VAT overnight then prices won't round to .99 until merchants (or Amazon themselves) change the base price again. I don't see the issue.
Usually in B2C prices are quoted and agreed upon as gross price (including tax). If the tax rate is lowered, this then raises the base price.
So it's unlikely their German prices would just take the same input as eg Dutch prices and changed the VAT around.