Just had to walk through the entire fricking application in my spare time to find this problem.....
Change the file "classes/Tools.php" and find the "public static function ps_round($value, $precision = 0, $round_mode = null)"
Add the following line:
if($precision == 0){ $precision = 2; } //Or any other number you want
Somehow the precision was always empty this fixed it for me.
Hope this helps atleast someone