er, 0 to 1e+9 inclusive
      <br />
      <code>rounding_mode</code> : <i>number</i> : integer, 0 to 8 inclusive
    </p>
    <p>
      Returns a BigNumber whose value is the value of this BigNumber rounded by
      the specified <code>rounding_mode</code> to a maximum of
      <code>decimal_places</code> digits after the decimal point.
    </p>
    <p>
      if <code>decimal_places</code> is omitted, or is <code>null</code> or
      undefined, the return value is <code>n</code> rounded to a whole number.
