Proxy / most visited sites per user (IP)?

I have been asked to implement some kind of way to see what users visit what websites while at work. (The management is worried by Facebook, but don’t want me to block it completely, only that it is used in moderation.)

So I was wandering can I implement something like that on appropriate Mikrotik device? Mikrotik has nice traffic graphing built in, so I was wandering about website hits.

Thanks