You can't change the estimated tax voucher amounts, even to round up. The software takes the estimated amount to avoid penalties and divides it by the applicable number of payments, but you cannot change the amounts of a voucher.
Alternatively, you can complete the short 1040-ES vouchers yourself and enter the amount you'd like to pay. You'll find the vouchers on the last pages, HERE.
Turbotax USED to let me round up the payment amounts to the nearest $10 or $100. Why can't I do that anymore?
You can round to the nearest $10 or $100. Go to Form View "Est Tax Options". It was a form just above the first 1040ES. I just did this so I know it is possible.
The online version of TT does not have a form-view option - so that suggestion won't work for me. My state program (Illinois) presented the option to round estimated tax vouchers before filing, but not the federal. (Both my federal and state were part of the TT online version.)
Once you print out the vouchers for Estimated Payments you can change the amounts on the vouchers.
If you would like you can pay your Estimated Payment online instead of sending in the vouchers