Assuming that all the calculations are done to a formula and quite likely performed by computer algorithms rather than humans it’s probably just a glitch. The software is probably supposed to round up and it hasn’t for some reason.
As is often the case in today’s corporate world the call centre staff have no idea what the answer is and have no appetite for finding out so they just try to fob you off and tick the box that says they have dealt with your enquiry.
Maybe they’ve been undercharging for years rather than overcharging.
In the big picture it doesn’t amount to a hill of beans but if it’s bugging you that much then good luck with your quest for the truth ?
If I seem a little strange, that's because I am.
Skoda Karoq SEL.