I don't know the real values or anything, but if i was to give some % based on my own experience i would say:

chance: 30% (most basic atks)

fixed: 50% (Utakata's standard atk, etc...)

high chance: 80% (yugito nii's standard atk, etc...)

very high chance: 90-95% (masked man & minato evading passives, etc...)

Certain hit: 100% (sage naruto standard atk, tsunade hokage mystery, orochimaru traitor mystery, neji GNW mystery, etc...)

Fixed chance won't be affected by combo stat and certain hit won't benefit from it as it's already 100%.