A rollover...as you put it...from a traditional IRA to a Roth is called a Roth Conversion. Which is taxed at the amount when converted...and is subject to a 5 year wait period before you can use it...or the gains from it. Or else there are penalties.
Oh, in that case, if you qualify, you can rollover, pay the taxes and hold for 5 years from the 1st of this year. Your year 1 would almost be over, so you have to wait before withdrawing for only about another 4 years and 1 month.
Here's some info: https://www.fidelity.com/learning-center/personal-finance/retirement/roth-ira-5-year-rule I've done 4 of them over the years. Personally, I found it best to open an individual Roth IRA for each one. 3 of them are now finished with the 5 year rule. If they were all in one, I would imagine Fidelity would be responsible for separating somehow in the one Roth. This way, when I withdraw, I know exactly where I can and cannot withdraw from.