croun:
functions with custom rounding
a rnd ("round") function to round up from 5, in positive and negative alike
a drnd ("down rounding") function to always round down, in positive and negative alike
a prnd ("physics rounding") function to round errors: if the first digit is a one or a two it rounds to the second digit, otherwise to the first.
a getk function to get the number of digits n in prnd was rounded to