If it's a chain, they aren't going to pay you under the table; under the table means they pay you in cash so there's no paper trail and a chain is usually a franchise and the franchise people would know/not allow that and the IRS knows how many employees a place needs to run, what they get paid (why wait persons in restaurants have to file with their tips; the IRS agents literally wait outside the restaurant and see how many people dine there on average and see the restaurant's books, etc. so know about how much tips the wait staff should be declaring). You would just be a contract employee and that way they would give you work in busy periods be able to have a "stable" of clerks able to come in and work on demand and they get a 1099.

It would depend on how much you worked for them when and how you had to pay taxes; I was going to work for H&R Block but it did not pay well; was mostly just a springboard for people to work for them a year or two and then "steal" away the customers who they'd seen/established a rapport for so they could do it on their own. But that year I was an independent contractor for several other jobs I'd set up (not H&R Block though) and did not pay taxes quarterly or do any of the things I should but the next year when I had a full-time job with benefits I went to one of my H&R Block classmates to have him do my taxes (I was too lazy) that I hadn't done and with penalties, etc. I think I had to pay a total of $131; if you don't make much money you aren't going to have to pay much but, if you don't make much money, the little you do have to pay will seem a lot