There may be other worms that you don't see in the stool that only seeing eggs in the stool sample under a microscope at the vet's can detect.
However for roundworms any over the counter med using pyrantel pamoate as the active ingredient should work. You dose by weight. A couple of name brands are Evict and Nemex but there are others also that use that as the active ingredient.
Its pretty safe and works against hook and rounworms you dose about 2 weeks apart for 2 to three times total over 4-6 weeks.
You can read about dog worms here
http://www.thepetcenter.com/exa/worms.html
Hope this helps you!
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