Tomato plants can have roots that grow as much as 2-3 feet deep. Especially in a nice, loose soil.
However, in something such as a container tomatoes, obviously the roots will go only as deep as the pot. ***c2-adsense-ad.shtml*** Raised beds are the same. The plant will grow usually to the depth of the bed...unless you tilled up some of the top soil before installing the raised bed.
With all of that said, don't forget about the distance tomato plant roots will grow laterally. Very easily one could have roots growing sideways a couple of feet.