I worked retail management for many years. I can tell you when I was the interviewer, I was less concerned with the answer and more concerned with the overall presentation. I hired many people who simply said I wanted work experience or I wanted a job for extra money. These are not "deep" answers, but each person presented themselves well, appeared heartfelt, sincere, and honest. They dressed appropriately (no shorts, tank tops, jeans, etc). They were friendly and pleasant.
Make a good impression, take a deep breath and be yourself. But, use the same manners you would with your grandmother. :)
Relax, you will do just fine.