123 to the nearest tens is ____.

To round off a number to the nearest tens, we need to check its units digit.
If the units digit is less than 5, we can make the units digit zero and keep the tens digit the same.
If the units digit is more than 5, we can make the units digit zero and add 1 to the tens digit.
In 123, 
$3 < 5$

$123 \cong 120$
Therefore, we can round 123 to the nearest tens as 120.