What is SGG's rounding calculation for mana?

Had some really bizarre behavior going on today in a war facing off against Onatel twice (before and after reset). At one point when viewing her debuff it said 25% of mana is stolen. What happens when that becomes a decimal, both for Onatel and the target?

Re-reading her ability afterwards (did not pull her in Jan on whenever it was) I see that it changes per turn until reaching 100% theft. Does anyone know what those values are?