Well, if I count the CFII as a passenger... 3/5 rounds up to 1, down to 0. If I don't count the CFII, 1/5 rounds to 0 anyway you look at it (normal rounding or rounding down).
The OP got his terminology wrong. "Rounding" has a formal mathematical definition. "Rounding down" has no formal mathematical definition that I am aware of. Rounding means to produce the nearest integer. That process yields a unique value for all fractions except N + 0.5, where N is any integer. At N + 0.5 the convention has been adopted to select the largest nearest integer (N + 1). So 3.5 rounds to 4, while 3.4999 rounds to 3.
One might use the phrase "round down" to identify the process of rounding the midpoint value (N + 0.5) to N rather than (N + 1). But one might also use the phrase as a synonym for truncating the number to the nearest integer (N + fraction) becomes N. In the first meaning 3.4999, 3.5, and 3.51 round to 3, 4, and 4; while in the second meaning they all "round down" to 3.
(I'm available for pedantry like the above at affordable values of $N.)
