Removing single handle faucet

I am trying to remove a single handle kitchen faucet. In the past, I have used an allen style wrench (that comes with the repair kits) through an access hole under the handle. But in this case, the allen screw head looks like one would if it were rounded out somehow. Is this some style of screw head that I haven't encountered before? It just seems unlikely to me that an allen head would round out like that.

I am trying to replace the o-rings in the spout which leaks out the sides.

If it sort of looks like a star, it could be what they call a Torx. They come in numbered sizes.

handle

It is probably an Allen screw, and because they have a small cross section, they will round out. But it could also be that your wrench is one size too small or metric, or the allen screw could be metric, and is not fitting perfectly.