Alot of dogs won't show symptoms of worms until they have had them for awhile or have so many of them. Your best way to go is to take in a stool sample for your vet to check to see if he has worms, alot of worm eggs can not be detected easily and he may still have worms. Your vet can determine whether he has worms and what type of worm he has if he has any.
Here is a link that tells you about the types of worms that dogs can get and they have some pictures of each type of worm. Tape worm segments do look like grains of rice though.
http://www.thepetcenter.com/exa/worms.html