PHP, 47 39 bytes

function a($b,$c){return round($b,$c);}

Try it online!

PHP, 16 bytes

16 Bytes if not a function

<?=round($a,$b);

Try it online!

PHP, 47 39 bytes

function a($b,$c){return round($b,$c);}

Try it online!

PHP, 47 39 bytes

function a($b,$c){return round($b,$c);}

Try it online!

PHP, 47 39 bytes

function a($b,$c){return round($b,$c);}

Try it online!

PHP, 16 bytes

16 Bytes if not a function

<?=round($a,$b);

Try it online!

PHP, 47 bytes

function a($b,$c){return number_format($b,$c);}

Try it online!

PHP, 47 39 bytes

function a($b,$c){return round($b,$c);}

Try it online!