Why the interviewer is asking this question: The interviewer is asking to align expectations for the role with your long-term expectations. While interviewers typically want solid alignment on near term (i.e. under 5 years) expectations, more latitude can and will be given for longer term goals.
If they don't want to give benefits to stocker and cashiers they should have part time hours and paid $17.50 per hour no benefits. Also how many teenagers would like a parttime job from 3 pm until 7pm and maybe get the pay they give their cashiers $8 -9 an hour.
Assume a retail worker makes $8 per hour for up to 40 hours. At time-and-a-half, his overtime pay is $12 per hour. If he works 50 hours during a busy holiday season week, he earns $320 in regular pay for the first 40 hours, plus $120 in overtime pay for the remaining 10 hours.