The easiest way to check for Tor traffic is to see if there are connections on ports 9001 (default entry port), 9030 (default directory port) or whatever other ports you have chosen besides the defaults. Running "netstat" from the command prompt (start->run->cmd ; at the prompt netstat) will show all open connections.
There are other options if you need/want more specific information. Personally, I configured my router for QoS scheduling but it also reports outgoing bandwidth and number of connections by the class of traffic (e.g., Tor, ssh, www, and whatever else I have configured).