### 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 $$18$$.

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 29 to nearest tens.

Estimating 29 to the nearest tens $$=$$ 30.