hum, si, sj: Use `--round=nearest` with `numfmt`(1)

hum, si, sj: Use `--round=nearest` with `numfmt`(1)

Default behavior is to round away from zero, that can be annoying if the
number for example is 1G+1, then it will round it up to 2G. It also
fixes rounding errors, for example would

    echo 1.07G | si

display the value 1070000001. See the log message for commit
`094a1e9e275d` ("Local/s10/mob: Fix rounding errors, use
`--round=nearest` in `numfmt`(1)", 2021-05-24) for more info about this
problem.

e501202c-b2b2-11ed-bb36-5582e081d110