By philipnorton42
on 11th April 2009

The JavaScript Math.round() function will round a decimal to the nearest whole number, but I found that I needed was to round a number to the nearest 10. So after a bit of thinking I realised that I could divide the value by 10, round it using the round() function and then multiply the result by 10.

So taking it a step further I decided to create a function that would round a number to the nearest 10, 100, 1000 or whatever value is entered. If this value is less than 0 then do the reverse by multiplying and dividing the number by the given value of accuracy. Here is the function.

function roundNearest(num, acc){ if ( acc < 0 ) { num *= acc; num = Math.round(num); num /= acc; return num; } else { num /= acc; num = Math.round(num); num *= acc; return num; } }

Here are some tests of the function.

alert( roundNearest(12345, 1000) ); // 1200 alert( roundNearest(12345.1234, -100) ); //12345.12

This function can be simplified a little by putting all of the calculations onto one line.

function roundNearest(num, acc){ if ( acc < 0 ) { return Math.round(num*acc)/acc; } else { return Math.round(num/acc)*acc; } }

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