Theory:

General rule for rounding:
  • If the number ends up with \(5\), \(6\), \(7\), \(8\) or \(9\), then round the number up (nearest tens).
  • If the number ends up with \(1\), \(2\), \(3\) or \(4\), then round the number down (nearest tens).
Example:
Consider the numbers \(13\) and \(18\).
 
Let us rounding the numbers to nearest tens.
 
Note that \(13\) ends up with \(3\) and \(18\) is end up with \(8\).
 
Consider \(13\),
 
Here the tens digit is \(1\), and the unit digit is \(3\), which is lesser than \(5\).
 
So leave the tens place unchanged and change the digits to the right of \(1\) to zero.
 
That is the rounding the number \(13\) results in \(10\).
 
Consider \(18\),
 
Here the tens digit is \(1\), and the unit digit is \(8\), which is greater than \(5\).
 
As the right of the tens digit is greater than \(8\), add \(1\) to it. That is \(1+1=2\).
 
Now change the digits to the right of \(2\) to zero.
 
That is the rounding the number \(18\) results in \(20\).
 
Here come the number line for the numbers \(13\) and \(18\).
 
Capture_1.PNG
 
It can be concluded that both \(13\) and \(18\) lies between \(10\) and \(20\).
 
The number \(13\) is nearer to \(10\) than \(20\), and the number \(18\) is nearer to \(20\) than \(10\).
 
Therefore, the nearest tens place of \(13\) and \(18\) are \(10\) and \(20\).
Thus, let us see the procedure for rounding the number to the nearest tens.
Step 1:  Find the digits in the tens place.
 
Step 2: Determine the digit to its right.
 
Step 3: If this digit is \(5\) or greater, add \(1\) to it. If it is lesser, then leave it as it is.
 
Step 4: Make the digits to the right of tens place to zero.
Now try to round off 157 to nearest tens.
 
Estimating 157 to the nearest tens \(=\) 160.