The main thing in this strategy is that your estimate is pretty close to the amount owed. So you may overshoot or undershoot, but likely by a pretty small amount, which is likely to make the difference owed small. I guess it could be considered a cost of filing taxes.

How much are the penalties?

If they are charging some absurd (say 20%) interest and you're off by 10k, you might pay them a few hundred in interest if the process is prolonged a month, which is on par with a tax prep service.

If you overpay they'll credit you next year. They're pretty lenient as long as your act promptly in good faith