Do they take your license number down when you buy ammunition and record how much you have?
There's actually a Police approved register sold by Zions Systems "FAR A1 Register of Ammunition Purchase and Sale" though dealers can use any method they like providing they capture the same information. The form requires the following details in order to comply
Date, Purchase / Sale, Handgun / Longarm, Name, Address, Licence/Permit No. Qty Ammunition, Manufacturer/Description/Calibre, Registration No. PTA No.
In answer to your question, Yes they should be recording the quantity but before getting all paranoid these records are held by the dealer and would only ever be inspected by the registry as a result of an incident investigation or dealer auditing. I keep my register secured in a well hidden location well away from any firearms or ammunition.