Why is this code yielding something like this?

I am using the following PHP code...

Code:

echo round(($satoshiValue/pow(10,8)),8);

When, $satoshiValue = 10000, result is 0.0001 as expected.

But, when, $satoshiValue = 10000000, result is 0.10000000000000001. Expected was 0.1 though.

Why is this happening?

p.s. I could not find a better place to ask this question on BitcoinTalk. So, asking it here. If mods think, it does not fit here, feel free to move.