Round number to 2 decimal places

Hi Forum,
I need to round a number to 2 decimal places within the Add Page Before record added and Add Page After record added Event.
I have carried out the following actions so far:
$testnum = '1.225';

echo "testnum: " . round($testnum,2) . "<br />";
This work 100% and displays 1.23
also
,2);

echo "testnum: " . $values["testnum"] . "<br />";
This does not work correctly and simply displays 1.22
Your urgent help to resolve this would be much appreciated.
Lisa