Whenever you create a new address on a Ripple wallet, the new address has a new destination tag, incremented by 1 from the previous destination tag. The main part of the address stays the same, but at the end you will notice that the address ends with ?dt=x (where x is a number that continues to increment with each new address you create).
You can then create an internal source document (such as a spreadsheet or db) to track which users are assigned which destination tag.
You would be able to track these in the wallet reports that you can run in the web interface; for each receive transaction, it shows the destination tag it was sent to. If you download the CSV version of the report, you would also be able to sort the transactions by destination tag in a spreadsheet program. One limitation to this, is that transactions that are transfers from one XRP wallet in your enterprise to another, do not reflect the destination tag on the wallet reports.