This solution requires Python 2.7. The rounding behavior changed from always rounding up at the half to bankers rounding in python 3.

Doesn't work for 4.25
For some reason round() rounds down for 8.5 but for all other x.5 numbers it rounds up. Tried in multiple editors. Bug in python?

Cool solution, solved this kata as my first cipher ever not nearly as smooth.

You can change the table to one line though. But don't know if it matters in terms of complexity.
(View solution)