ATM’s in Ljubljana Slivenia

If you make sure to reject the option of being charged in USD (or what ever your home currency is), you will get the lowest possible rate. That does not mean you will not be charged a local ATM usage fee (which will be disclosed) or your own bank's foreign transaction fee (often 3%) or your bank's out-of-network fee. If possible, use an actual bank ATM.

If you were to opt to be charged in USD, it is then the bank, and not the network that will determine the exchange rate and it will NOT be in your favor.

Sam is totally correct, but I would also note that you should not need very much cash
on a trip these days, so a 1-2% difference in an exchange rate is not going to be very
much $, and may not need to be that stressful a concern.

Be sure to use an ATM at an actual bank for the best rates.