Setting snapToDataPoint to true automatically snaps crosshair to nearest data point, otherwise follows mouse co-ordinates.
Default: falsevar  chart =  new  CanvasJS.Chart("container",
{
 .
 .
axisY:{
	crosshair:{
		 enabled: true,
		 snapToDataPoint: true,
		.
		.
	}
 },
 .
 . 
});
chart.render();