GPS plays an important role not just in setting location, but the whole GPS system is powered by clocks. Your GPS receiver uses tiny time differences in signals it receives from multiple satellites to measure distances. The GPS network is a fantastic source of an incredibly reliable clock, it is one of the most reliable clocks in the world. Many banks, broadcasters, IT companies, and other business that rely on time use GPS for this purpose.
However, I don't believe all ATM bank machines use GPS but if they did it would be to timestamp the transactions.
There is another acronym of ATM which uses GPS however. Asynchronous Transfer Mode is a telecommunications network system that was widely used before the dominance of IP that we have now. To get these ATM systems correctly synchronised they need a reliable reference frequency and the GPS clocks can provide that as well.