I don't know about every single ammo purchase (that would be a little hard to implement), but I've been saying that about the NICS check for years.
I probably should have conditioned that on every ammo purchase using plastic. It would be easy to record ammo purchases on a card because I believe the NSA archives every electronic purchase any and everyone makes as part of their banking monitoring. Later on a simple database query to list all purchases of ammo for a certain time period would not be hard at all.