They're allowed to ask, but you're not required to answer.

"By marking a ballot in private!" is an acceptable answer to "how are you voting" in my opinion.

As far as I am aware, yes they can ask, but you also have total freedom in not answering! You can respond by saying "I'm not comfortable talking about that right now," "I don't want to talk about that," or maybe "I'd rather not say."

If they keep pushing after that, you can repeat those lines just to emphasise your point and try to change the topic. Ask them something about themselves to put the ball in their court, so to speak.

You are definitely not obligated to tell them how you will be voting. I don’t believe it’s illegal for your coworkers to ask how you will vote, only for them to tamper or have access to your ballot. If you are comfortable, just tell them you’d rather they not ask. They are likely just doing it so they can track the ballots and have a general estimate of the election results.