function toCurrency(val,currency) {
val=(val+"").replace(/\,/g,"");
return  ((currency? currency:"") + 
(Math.round(val*100) + 
(val<0?-0.1:+0.1))/ 100).replace(/(.*\.\d\d)\d*/,'$1');
}

Calling the function:

<input type="button" name="Button" value="Convert" onclick='document.getElementById("js").innerHTML=toCurrency(2.3467,"£")'>

<span id="js"> </span>