Those are T. hengeli. They are not suitable for a 10 gallon tank, I'm afraid. That's why Byron suggested taking them back to the store.
One of the most important lessons in fish keeping is don't believe anything a shop worker tells you. Most of the workers haven't a clue about fish keeping and will say anything to make a sale. If they told you the T. hengeli are suitable for 10 gallons, that demonstrates the point.
The other alternative is to upgrade the tank - you need one at least 24 inches long, and 10 of each of the fish you have.
The reason they are sticking together is because they are stressed. Fish which are not stressed go their separate ways. They are new to the tank, the #1 reason they are currently stressed. It takes several days, sometimes a few weeks, for fish to settle in. They've just been through a very stressful time. member Colin_T has written about this
If any of you have wondered how aquarium fish get to the local pet shop, the following will give you some insight as to what they have to go through to get from the fish farm where they are bred and raised, to the pet shop where you can buy them. The stress they go through is quite...
www.fishforums.net
There are also not enough T. hengeli which makes them feel stressed. Shoaling fish are programmed to expect a large group. Think of it like this. In the wild they live in groups of hundreds. When there are not enough of them their instincts tell them that something has eaten the rest of the group and they're next on the menu. They don't know there's no predator lurking outside the tank.