Round a number up to a significant number of digits.

gistfile1.txt

function ceilToSignificant($number, $figures) {
   $digits = ceil(log10($number < 0 ? -$number : $number));

   $power = $figures - (int) $digits;

   $magnitude = pow(10, $power);

   $shifted = ceil($number * $magnitude);

   return $shifted / $magnitude;
}