If I did a $3000 Roth Conversion and had $300 taxes taken out, what amount do I enter when the program asks How Much of the $3000 was converted to a Roth ? Do I enter the $3000 or $2700. $3000 came out of my traditional IRA but only $2700 ended up in my Roth account.
See @dmertz answer. He is a recognized expert in retirement tax law.
Since you did not substitute other funds to replace the $300 that was withheld for taxes, only $2,700 was converted. Telling TurboTax that you converted $3,000 implies that you substituted other funds within 60 days of the distribution from the traditional IRA and you ended up with $3,000 moving to the Roth IRA.
If you are under age 59½:
If you were over age 59½ at the time of the distribution from the traditional IRA:
Note that telling TurboTax that you converted $3,000, which is incorrect, won't produce an incorrect taxable amount on line 4b of your Form 1040, but it will cause TurboTax to generate an incorrect Form 8606.