That, once again, depends on the species. Most species of Betta are mouthbrooders, and all other Gouramis (including the remaining bettas) make bubble nests, both of which are way to protect fry. Cichlids will also protect their fry, or at least some of them.
But, if the store told you they were male and female, I'd buy another female, as they're probably livebearers, so just put them together. Females can get stressed out by too many males, so get double the females than males.
Also, has the original poster even been on since this topic was started?
;.;LEEWhit;.;, goldfish can breed, but they need a pretty big tank because they need to grow to at least a foot (which can be prevented in a small tank) and you'll need a male and a female.
So it's probably a guppy or something.