code: function normalizeTickInterval(interval, multiples) {
  			var normalized, i;
  
  			// round to a tenfold of 1, 2, 2.5 or 5
  			magnitude = multiples ? 1 : math.pow(10, mathFloor(math.log(interval) / math.LN10));
  			normalized = interval / magnitude;
  
  			// multiples for a linear scale
  			if (!multiples) {
  				multiples = [1, 2, 2.5, 5, 10];
  				//multiples = [1, 2, 2.5, 4, 5, 7.5, 10];
  
  				// the allowDecimals option
  				if (options.allowDecimals === false || isLog) {
  					if (magnitude === 1) {
  						multiples = [1, 2, 5, 10];
  					} else if (magnitude <= 0.1) {
  						multiples = [1 / magnitude];
  					}
  				}
  			}
  
  			// normalize the interval to the nearest multiple
  			for (i = 0; i < multiples.length; i++) {
  				interval = multiples[i];
  				if (normalized <= (multiples[i] + (multiples[i + 1] || multiples[i])) / 2) {
  					break;
  				}
  			}
  
  			// multiply back to the correct magnitude
  			interval *= magnitude;
  
  			return interval;
  		}
docs: Take an interval and normalize it to multiples of 1, 2, 2.5 and 5
  @param {Number} interval