Well, that's a function of the 'true price' being measured in a different currency than the one you're paying in. Some retail businesses that accept foreign currency rectify this with a flat exchange rate.
For example, in Canada businesses (at least on Southern Ontario) will generally accept payment in USD instead of CAD, but they tend to have a flat exchange rate (e.g. 1 USD = 1 CAD or 1 USD = 1.10 CAD). If they priced the exchange rate to the current exchange rate as measured by some currency exchange, that would be different.
You run into this same issue when using a US credit card in Canada. The credit card company will exchange (and usually charge an extra ~1% charge). IIRC, they use up-to-date exchange rate info, so technically the price in USD is constantly changing.
For example, in Canada businesses (at least on Southern Ontario) will generally accept payment in USD instead of CAD, but they tend to have a flat exchange rate (e.g. 1 USD = 1 CAD or 1 USD = 1.10 CAD). If they priced the exchange rate to the current exchange rate as measured by some currency exchange, that would be different.
You run into this same issue when using a US credit card in Canada. The credit card company will exchange (and usually charge an extra ~1% charge). IIRC, they use up-to-date exchange rate info, so technically the price in USD is constantly changing.