Three variables to consider.

1- is the calculated length the minimum, maximum or optimum. Optimum means the spoke will reach to less than 1mm short of the top of the nipple when the wheel is finished.

2- how much over travel is available in the spoke and nipple thread, or how far above the top of the nipple can the spoke go if it's too long. Typically this is 2-3 millimeters, but varies with brands.

3- are you building hollow rims where spokes going beyond the nipple don't matter, or single wall rims where you'd have to grind off any excess.

Answering those questions for yourself will tell you how much fudge factor you have in either direction, and which is the best size to go with if you don't want to deal with two.

Generally I prefer to use only 2 spoke lengths, the sa;e for left rear and front, and usually 2mm shorter for right rear. That's no big deal because I usually also use a stouter spoke on right rear, ie. 14/16 for right rear, and 14/17 for left and front.