So my German "sister" is visiting me, and today she used her European Mastercard (Santander Bank) at the Ross Dress For Less - and "Dynamic Conversion" happened - from Dollars to Euros. She purchased $128.75 but they charged her EU 117.97 Euros. According to her sales slip, the rate was "0.9163, including a 3% margin."
She was asked by the register computer sign-in tablet if she agreed to the Euro rate, and out of habit she chose it. This was the first time I have seen this. She had actually meant to use her Bank of America (Dollars) Debit card (we share a joint bank account in the USA for the times she comes to visit me. She wires her money from her bank to our Bank of America account, and it costs her around $20 to do this; I get notice of it because it's a joint account, and then it's easy to track her spending while she's in California.