When rounding to integers, look at the first decimal. If that digit is $0,1,2,3,$ or $4,$ round down, and if it's $5,6,7,8,$ or $9,$ round up. See the following examples.

Number	$\approx$
$639.693$	$640$
$2.3$	$2$
$90.6$	$91$
$16.06$	$16$