Do I need to mail a voucher if I paid my taxes electronically?
No. If you paid your IRS or state taxes electronically (direct debit, credit card, EFTPS, etc.) there's no need to print out and mail a payment voucher.
Sending in a payment voucher without an accompanying check or money order is a waste of postage and may cause confusion and extra work for the government.
Now, if you paid your taxes outside of TurboTax (for example, through EFTPS or a third-party payment processor), you may have had to select the check payment option as a way to get past the TurboTax payment screen. In this case, you'll get instructions to print out a payment voucher, which you can safely ignore.