I avoid alloy nipples, using best quality brass nips I can find.
I use as many spoke calculators as I can find (often plugging in numbers to as many as 6 for any given build) cause tho most are very close there's always some "interesting" outlying variation...then I average the results.

Despite this I have had too many wheels build up with slightly loose spokes, especially on the rear wheel where calculators seem to have trouble with the different length requirements for dishing, and so:

I always round DOWN.

YMMV