Time to look for another job.
In the past, the hardest part for me was not letting my anger at their arrogance rule my response. Their belief that they have all the answers because some book says so is stupid beyond comprehension but it's a stupidity that is not necc. their fault.
Now I often respond with a question like "do you think other beliefs are also valid"? or "can we make a better world by accepting others religious views" etc.
Mose christians are christian because they have been taught not to question. Actually I believe they need our help. Questioning as I would guess you know, helps us find the truth.

Go on a murder spree just to prove them right and to let them know you truly live by biblical principles. ?

I think others here have more helpful answers.

It’s tough, depending on the rest of the culture. If you feel you’ll be discriminated against, I wouldn’t be open about it. Maybe ask them questions about certain things that you know are difficult to believe or hypocritical in their holy books. Just be your good self.

Sorry for your dilemma. Wish I had something helpful to offer.
I'd be quietly looking for other employment.

Disgusting people.

I'd make myself indispensible to them, be their dream employee so long as they treat you well (and it's not treating you ill merely to have a different view of reality than you).

Then if it comes out at some point that you're a reprobate, it will at least be fun to watch the resulting cognitive dissonance between the respect you're earned and their preconceptions of atheism, create a back hole that makes their heads implode.

My main client is helmed by a couple of conservative Catholics who are for some reason are turning over at least the sales management side of things to a fundamentalist Christian, but in 12 years they've never figured out that I'm an atheist. They may suspect I'm not very observant, and they certainly suspect I'm way more liberal politically than they are, but I work far more miracles for them than their god ever does, and I'm part of their technological "secret sauce" so they just have to suck it up and tolerate me. Besides, they are professional enough to know better than to pry into personal matters.

As for the fundie, he's dumb as a post and since I'm a former fundie myself I have dropped a couple of hints that has him believing I'm just like him. He came to us via an acquisition though and I'm 90% sure his days are numbered, since after buying his shitty little company we figured out all his tech was a combination of smoke and mirrors and total mismanagement of his development team (not to mention some highly questionable accounting) and I think the only reason he hasn't already been shown the door is that the purchase came with some kind of commitment to his employment that they're running out the clock on. But just to be safe, I'm not above allowing him to think I'm a fellow believer. It didn't take much, just nodding sagely and sympathetically in the right places. These guys have been hoodwinked by their preachers for so long, they don't know how easy they make it. I am just careful to only allow him to mislead himself about my motivations and reasons for agreeing with him. In other words he'll say something like "It's really important to be honest" and of course I totally agree with that, but I agree with it using evangelical non-verbal virtue-signalling cues and he assumes I think it's important to be honest to avoid god's displeasure, rather than because it's just the right thing to do.

If you didn't come from the inside of the funhouse hall of mirrors that is Christian fundamentalism, then "don't try this at home kids" but if you do ... have fun with it!

If it's a small mom and pop business, then you'll have to decide how badly you want to keep your job. If you do, you will have to play along until your personal ethics won't allow you to. You can try to calmly and in a non threatening way that you are an athiest. But, be prepared to be taken negatively.

If it's a medium to large business that has an hr department, talk to them about it.