Rounding 3.221 to the nearest hundredth would be 3.22.
Why?
Well, 0-4 doesn't have power to round up. If the '1' would be at least a 5 or higher you would be able to round it up, but in this case it wasn't so it turned to a 0. The hundredth would be the 2nd place before the decimal. The decimal acts as a mirror and it also acts as the single-digit number.
Ex:
H= Hundred, T= Ten, O= One, D= Decimal, Tth= Tenth, Hth= Hundredth
H|T|O|D|Tht|Hth
1 2 3 . 4 5 = 123.45
Remember;
0-4 - doesn't have power to round up.
5-9 - has power to round up.
Hope this helps!~