In Mexico I use cash far more than I do in the US. Most businesses accept veedit cards, but a 5% "commission" is not unusual. I now know to ask before I pay... although you learn when to expect the extra charge after a ehile (a nice restaurant wont add the charge).
It seems only the utility companies around here charge convenience fees to pay online. They all have third party payment companies that handle their payment sites. The credit card co's, hospitals and Dr.'s do not charge any fees to pay online. The credit union didn't charge a fee to pay the car loan either.