Rounding to the nearest 10, 100 and 1000
In a nutshell
Rounding numbers makes them much easier to work with. It also allows you to estimate answers to long, tricky calculations.
Rounding to the nearest 10
Definition
Rounding to the nearest ten means to round a number up or down to the nearest multiple of ten.
PROCEDURE
1.
 Look at the digit in the ones column. 
2.
  If the value is $0,1,2,3$ or $4$: round down to the nearest multiple of ten.
 If the value is $5,6,7,8$ or $9$: round up to the nearest multiple of ten.

Example 1
Round $72$ to the nearest ten.
Look at the ones.
The digit in the ones column is $2$.
Round down to the nearest multiple of ten.
$72\rightarrow\underline{70}$
Tip: Remember, a multiple of ten has a zero in the ones column. If you already have a zero in the ones, your number is already rounded!
Rounding to the nearest 100
Definition
Rounding to the nearest hundred means to round a number up or down to the nearest multiple of $100$.
PROCEDURE
1.
 Look at the digit in the tens column. 
2.
  If the value is $1,2,3$ or $4$: round down to the nearest multiple of $100$.
 If the value is $5,6,7,8$ or $9$: round up to the nearest multiple of $100$.

Example 2
Round $673$ to the nearest hundred.
Look at the tens.
The digit in the tens column is $7$.
Round up to the nearest multiple of $100$.
$673\rightarrow\underline{700}$
Rounding to the nearest 1000
Definition
Rounding to the nearest thousand means to round a number up or down to the nearest multiple of $1000$.
PROCEDURE
1.
 Look at the digit in the hundreds column.

2.
  If the value is $1,2,3$ or $4$: round down to the nearest multiple of $1000$.
 If the value is $5,6,7,8$ or $9$: round up to the nearest multiple of $1000$.

Example 3
Round $1629$ to the nearest thousand.
Look at the hundreds.
The digit in the hundreds column is $6$.
Round up to the nearest multiple of $1000$.
$1629\rightarrow\underline{2000}$