How do you round 105 to the nearest hundred?
Showing what I call the cut off point (in red)
In your mind only write the number as:
The digit to the right of the cut off point is less than 5 so we round down. That is, change all the digits to the right of the cut off point as 0 so:
105 is 100 to the nearest one hundred.
If the digit to the right of the cut off point had been 5 or more then we would have 200 to the nearest one hundred
Suppose it had been 163
6 satisfies the condition of 5 or more so the digit to the LEFT of the cut of point has 1 added to it.
Consider to the nearest 10