We do not have all the details.
Did you back into the way as carts were moving?
Did you force the employee to devite from his original path?
Did you stop to let the employee move passed your car with the carts?
We'd need details to know if the employee did a bad job at pushing his carts or if you are at least partly responsible for backing into the carts.
As for the employee, what did you expect? Even if you believe he is responsible for what happens, what good could possibly come out of screaming at that kid? He works for a minimum wage, doing possibly the worst job in the entire place, in the middle of a parking lot filled with people who are too much in a hurry to give a damn about him... Before you even begin to talk to him, he's probably not a very good mood. If you were young, broke and pushed carts for a living, I am sure you would have insulted the client too. Not that it is sensible, but it certainly is predictable.
Besides, how would you react if you were sitting behind that desk, honestly? An angry client marches into your office, telling you that the store will have to pay for damages and suggested or even requiring that the employee be fired. Assuming that kid is not so incompetent he cannot push carts and can manage the simple job of arriving on time, you would rather not fire a perfectly good employee over someone's angry request. If you treated the manager in any way similar to the way you treated his or her employee, you deprived yourself of any chance that he or she would help you.
Now, if you want to do something, call your insurance. They likely will hold you responsible, ask for a small fee -- whatever the amount is defined in your contract --, pay the balance and you might get a small hike on insurance costs. Next time, be more careful and if you still get into an accident, try to express your anger in a more civil manner. Usually, you do not make people likely to cooperate by pissing them off.