I've always seen CBG's and CBU's tuned in fourths. You can tune ukes and guitars in fifths but it is rare. Tenor guitars are probably tuned in fifths most of the time.
I’ve been looking at three string cigar box guitars and most seem to be tuned as GDG, or similar tuning. Often played with a slide. Check out https://www.cigarboxguitar.com/knowledge-base/5565/