Wanted to pick the C&V mental collective's "hive mind" here, as I'm very new to building wheels from components.

I'll be building a new wheelset in the (hopefully) not too distant future, and have everything I need to lace it less the spokes. This includes purported dimensions on the hubs and rim ERDs, so I've done preliminary calculations for spoke lengths. (I will of course physically verify these dimensions against actual measurements and re-run the calculations prior to "pulling the trigger" on any spoke order).

Preliminary calculations from Karl Stoerzinger's online version of Freespoke and UBI's online spoke calculator agree. Given this, I'm fairly sure I'm entering the data correctly in both (the data is auto-populated on Freespoke, as the hubs I'm planning to use are in that version's integral database).

Three of the spoke lengths are slightly over an even mm (2XX.1mm or 2XX.2mm). Being inexperienced, it seems to me that I should round these down, especially given the fact that spokes stretch slightly when under tension.

However, the fourth calculated spoke length is just under an even mm - specifically, 2XX.9mm. Would I be best served to round these up or down?

Thanks in advance for any advice.