How to make number_format() not to round numbers up

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I would like to return a price using number_format(). I have this number:\[code\]$number = '10.594312';\[/code\]And then I have its doube:\[code\]$doube = '21.188624';\[/code\]After using number_format($double, 2, ',', ' ') I get:\[code\]21,19\[/code\]But what I want to get is:\[code\]21,18\[/code\]Any ideea how can I make this work? Thank you.