<?php

echo round(90.00 + 9.71, 2), PHP_EOL;
echo sprintf('%.2f', (90 + 9.71)), PHP_EOL, PHP_EOL;

for ($i = 6; $i <= 24; ++$i) {
    ini_set('precision', $i);
    echo "Precision {$i}", PHP_EOL;
    echo round(90.00 + 9.71, 2), PHP_EOL;
    echo sprintf('%.2f', (90 + 9.71)), PHP_EOL, PHP_EOL;
}