Everyone knows about and uses Math.round(), Math.ceil(), and Math.floor(). They’re great, but what if you don’t want to round to the nearest whole number? For instance, you might want to round to the nearest even number, or even a fractional value like the nearest tenth. The following functions make rounding in ActionScript 3 a lot more robust:

package com.joshtynjala.utils
{

/**
 * Utility functions for the manipulation of numbers.
 */
public class MathUtils
{
	/**
	 * Rounds a target number to the nearest multiple of another number.
	 * @see Math#round
	 */
	public static function roundToNearest(numberToRound:Number, nearest:Number):Number
	{
		return Math.round(numberToRound / nearest) * nearest;
	}

	/**
	 * Rounds a target number up to the nearest multiple of another number.
	 * @see Math#ceil
	 */
	public static function roundUpToNearest(numberToRound:Number, nearest:Number):Number
	{
		return Math.ceil(numberToRound / nearest) * nearest;
	}

	/**
	 * Rounds a target number down to the nearest multiple of another number.
	 * @see Math#floor
	 */
	public static function roundDownToNearest(numberToRound:Number, nearest:Number):Number
	{
		return Math.floor(numberToRound / nearest) * nearest;
	}

	/**
	 * Rounds a target number to a specific number of decimal places.
	 * @see Math#round
	 */
	public static function roundToPrecision(number:Number, precision:int = 0):Number
	{
		var decimalPlaces:Number = Math.pow(10, precision);
		return Math.round(decimalPlaces * number) / decimalPlaces;
	}
}

}
/*
Copyright (c) 2007 Josh Tynjala

Permission is hereby granted, free of charge, to any person
obtaining a copy of this software and associated documentation
files (the "Software"), to deal in the Software without
restriction, including without limitation the rights to use,
copy, modify, merge, publish, distribute, sublicense, and/or sell
copies of the Software, and to permit persons to whom the
Software is furnished to do so, subject to the following
conditions:

The above copyright notice and this permission notice shall be
included in all copies or substantial portions of the Software.

THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND,
EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES
OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND
NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT
HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY,
WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING
FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
OTHER DEALINGS IN THE SOFTWARE.
*/

I’ve used various versions of this class on many projects, and the functions will always be in my toolbox. You can download the class, and use it under the terms of the MIT License.