Yeah, I just do the quarterly estimated payments. If your business is constant (not growing) it's easy to handle via extra withholdings. If you are growing, they at least make it easy so that if you pay an estimated tax that matches the prior years tax owed (paid quarterly) you avoid any penalties, even if you have to make a lump payment to settle up the difference when you do your taxes at the end of the year.

We have a pretty sophisticated business intelligence platform written in R that gets us estimated revenues within 10%, so I know how to budget through the year for taxes owed. I just pay my known quarterlies and keep enough in the bank to handle the remainder at year end.