There's a bunch of them, but the tip offers are usually on the newer touchscreen (probably android based) ones.

The old ones (never seen the tip option on those... for now): https://www.simple-shop.si/en/pos-terminal-tcpip-en and eg https://www.unicreditbank.si/si/podjetja/upravljanje-z-denar...

The new ones: https://www.sumup.com/sl-si/karticni-citalec-terminal/ and https://besteron.com/si/pos-terminali/ (both support tips) + many other in similar designs (full front touchscreen)

I don't think square supports slovenia for now, but POS vedors add the tip option, and our restaurant owners enable it, because it doesn't cost them anything, any many (especially foreign) guests "feel bad" for choosing the zero on the screen.

Thank you.