Let's do some math ..  Rounding examples of 7 random hypothetical purchases:
Case	Tag   Price	Sales   Tax %	Raw Total   Incl. Sales Tax	Rounded   to Penny	Rounded   to Nickel	Rounded   to Dime
Purchase #1	$22.39	9.703%	$24.5625	$24.56	$24.55	$24.60
Purchase #2	$72.54	11.792%	$81.0939	$81.09	$81.10	$81.10
Purchase #3	$187.30	6.649%	$199.7536	$199.75	$199.75	$199.80
Purchase #4	$82.64	5.178%	$86.9191	$86.92	$86.90	$86.90
Purchase #5	$152.52	3.149%	$157.3229	$157.32	$157.30	$157.30
Purchase #6	$35.55	6.509%	$37.8639	$37.86	$37.85	$37.90
Purchase #7	$51.46	11.648%	$57.4541	$57.45	$57.45	$57.50
7 purchase totals =	$604.40		$644.9700	$644.95	$644.90	$645.10