Well honey, 621 rounded to the nearest ten is 620. Why? Because that's just how rounding works, sweetie. Don't overthink it, darling. Just remember, math is like a good bra - it's all about support and sometimes a little rounding up or down.
When rounding 621 to the nearest ten, you look at the digit in the tens place, which is 2. Since 2 is less than 5, you round down, making the tens digit 0. Therefore, 621 rounded to the nearest ten is 620.