It doesn't matter how you pay it. Uber is on your 1040 just like your W2. If its easier to just have your day job take out more federal and state tax, do that. Yes, you can pay the IRS online anytime you want. Estimated taxes don't need to be overly formal. If you get some cash and want to pay, just do it. You can do it 4 times a year, 20 times, or 1 time.
