Basically, rounding decimals is like basic rounding, but evolved.

Basic rounding :

Let's say you want to estimate a problem. You would need to round.

Let's use 34 for example.
Anything 4 and under would round off to the nearest hundred, ten, or thousand. In this case, the '4' in 34 would round into 0.
Now our number is 30.
Anything 5 and above round to the nearest ten, hundred, or thousand.

Now let's use the number 35 for example. The five must be rounded up, so it rounds into 10. Our number is now 40.


Rounding decimals :

All you need to do is round every number from the start.
Like this example.

3.67 = 4.00
3.23 = 3.00

But sometimes, you might need to round to the nearest tenth, or hundredth.
You only have to round the decimal numbers up or down.
Like this alternate example.

3.67 = 3.70
3.23 = 3.20

external image 6de4e05d-67c5-442c-a373-491d693f878c.gif
^ Let's say around there is 0.5. It would round to 1.0.