You can easily find US based banks and ATM near you with your mobile phone using zip code or actual address. Search results will provide both maps and directions.
All banks have their own forums/commenting/rating systems.
It is a proximation. Each zip code gets a latitude and longitude, for which I guess is at the center of that zip code region. Then you can compute the distance from that center to bank location, or radius to be exact. So distance info is very rough estimation.
If you want to know the exact direction to the ATM/bank location, you should use "street address" instead of zip code, the google direction will give you turn-by-turn direction to the bank.
