math - Get next bigger/smaller number with a given precession -

having double precision number , desired rounding number, how next bigger/smaller rounded number ?

sample

n = 10.476 prec = 0.25 smaller = 10.25 bigger = 10.50  n = 0.837 prec = 0.005 smaller = 0.835 bigger = 0.840 

def round_smaller(n, prec)   (n / prec).floor * prec end  def round_bigger(n, prec)   (n / prec).ceil * prec end