Something still uses it: prices, shipping rates, product feeds, markets, store settings, or an active Gift Card with a balance in that currency. Delete is also unavailable while automatic exchange rates are on. Why can't I disable or remove a currency?.

Can I use automatic rates with currencies I already added?

No. Automatic exchange rates can be turned on only when the store has no additional currencies. Delete them first, turn on Use automatic exchange rates, then switch the currencies you want back on in the list. Exchange rates and rounding.

Do customers pay the rounded price?

Yes. For prices converted from your base currency, the rounded amount is what customers see and pay. A price you enter for a currency is used exactly as entered, and the base currency is never rounded.

Why can't customers see a currency I added?

Customers see an added currency only after you assign it to their country in a market. Currencies across markets, products, and checkout.

Does changing an exchange rate change past orders?

No. Orders are recorded in the currency the customer paid in, with base-currency amounts fixed when the order is placed.