Hi, Mookie.
For the past few years, I've used only the Basic versions of Quicken and TurboTax. Maybe the Premier versions are different. I assume that you also are using Quicken, although you didn't say that.
In Quicken, when I sell stock, especially one where I have multiple lots - and most especially when I'm selling less than all my shares - I click the Specify Lots button on the Sell transaction screen. Then, for FIFO, I start with the oldest lot and just keep clicking to add the next oldest lot until Quicken says I have enough to equal the number of shares sold; the last lot probably will be only a part of the shares in that lot. The major advantage of this is that Quicken takes care of any rounding issues. This would be especially useful for something like fractional shares in a DRiP.
Then, to get the information from Quicken to TurboTax, Import the information into TT. You could print out a capital gains report from Quicken and enter the details into TT, but there would still be the risk of rounding errors. However, if you enter the actual dollars of basis that Quicken reports, and the actual dollars of proceeds from the sale, your reported gain should be correct, even if the number of shares is off slightly. You pay tax on the dollars of gain, of course, not on the number of shares.
RC