No idea. We probably had a period where we traded a lot with the French and got influenced by the vigesimal system that way, creating the abomination of a Frankenstein monster we have today.
The reason is that the Danish numbering system is based on a vigesimal (base-20) system instead of the decimal system. Why is a good question but it might have been influenced by French during a time where numbers from 50-100 is less frequently used, making them prone to complexity. The fractions simply occur since you need at least one half of twenty (10) to make the change from e.g 50 to 60 in a 20-based system.
Even worse. 90 in old Danish is "halvfemsindstyve" but it is rarely used today. The "sinds" part is derived from "sinde" means multiplied with but it is not in use in Danish anymore. That leaves halvfems, meaning half to the five (which is not used alone anymore) and tyve meaning twenty (as it still does).
We are in current Danish shortening it to halvfems which actually just means "half to the five" in old Danish (4.5) to say 90. 92 is then "tooghalvfems" (two and half to the five, or 2+4.5). The "sindstyve" part (multiplied with 20) fell out of favour.
So we at least have some rules to the madness. Were just not following them at all anymore.
Edit: Minor old Danish math correction.
Hvis det er neat whiskey så tyer jeg også selv oftest til en single malt Scotch, det er bare bedre ;)
En Bourbon har dog en sødme og nogle noter af vanilje og nødder som gør dem særdeles velegnet til cocktails. Årsagen er bl.a. det tørre klima de laves i, hvilket der ikke er mange steder i verden der kan replikere. Man kan måske kompensere med fx lidt nødde bitter sammen med en canadisk whiskey, men det får jeg testet i weekenden.
We actually still say "halvanden" in Danish too. Everything else is not used (except for halvfems which means 90...)