I checked ATM transactions (about a dozen) over the last couple of months; all of them show up as being processed on the MAC network (Withdrawals were in Sterling, Euros, and Czech Crowns).

It looks like there is usually a 1% surcharge, although there were a couple of instances where there didn't appear to be any surcharge or it was an odd percentage (0.5% in one case).

I used www.oanda.com as the source of the f/x rate. I'm not sure what day's f/x rate is used (day of withdrawal, posting to account, what happens on weekends).

It's helpful to know that ATMs are subject to the fee.

At least the banks that dispensed the cash did not charge a fee for using the ATM machine.