I have to agree. They paid the lower exchange rate out of convenience because they didn't want to go to a cambio. I expect places to have a lower exchange rate then at the cambio. That's why we use JA$. Granted, I would assume 100:1 if I had to guess but 95:1 is reasonable enough. They should put the total on the bill in US$ and JA$ or at least put the 95:1 exchange rate for US$ on the bill so you don't have to guess. When in doubt ask.