Divide by 10000, use floor
to round down to an integer, then multiply by 10000:
$x = 146740;
$x = 10000 * floor($x/10000);
Or subtract the remainer:
$x = 146740;
$x = $x - ($x % 10000);
To extend this to 1 million, you can do:
if ($x > 1000000) {
$divisor = 1000000;
} elseif ($x > 10000) {
$divisor = 10000;
} else {
$divisor = 1;
}
$x = $x - ($x % divisor);