Magento change currency format

/lib/Zend/Locale/Data/en_US.xml

<numbers>
    <currencyFormats>
        <currencyFormatLength>
            <currencyFormat>
                <pattern>¤#,##0.00(USD);(¤#,##0.00(USD))</pattern>
            </currencyFormat>
        </currencyFormatLength>
        <unitPattern count="one">{0} {1}</unitPattern>
        <unitPattern count="other">{0} {1}</unitPattern>
    </currencyFormats>
</numbers>