In regards to what type of knife might get you fired, I think you might be asking the wrong people, since none of us here are in a position to fire you.
I would suggest consulting with your superiors for recommendations. Or, before buying a knife for work, get pictures off the internet and show them the knives you are interested in and ask them what is acceptable. You wouldn't want to spend a stack of money on a new knife for work, only to find out you can't carry it at work, or get fired for bringing it to work.
It's very common for different people to have very different perceptions of individual knives. Knives that may appear completely harmless to members of this forum might look like weapons to the people whose opinions count the most- your bosses.
Something else to consider, if you choose a fixed-blade, your bosses might not want employees walking around the store openly carrying a knife. And depending on where you live, it might be illegal to carry a fixed-blade concealed, even at work.
Good luck in your search. And congrats on the new job.