What's your problem ? Just pay the seller
in yen.

You can't expect a shop, in another country,
to deal in your currency and above all to
be up-to-date with the exchange rate. (even
if some are...)

If you want to buy from a shop in Japan, pay
them in yen. It's a lot of bother for the shop
when you want to pay in another currency.
For one things, they exchange rate my drop
while they wait for the paiement and so they
will gain less.

Cheers,
Yann Stettler