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	$50.58	8.229%	$54.7422	$54.74	$54.75	$54.70
Purchase #2	$152.91	12.768%	$172.4335	$172.43	$172.45	$172.40
Purchase #3	$195.52	12.466%	$219.8935	$219.89	$219.90	$219.90
Purchase #4	$177.58	13.448%	$201.461	$201.46	$201.45	$201.50
Purchase #5	$51.45	5.468%	$54.2633	$54.26	$54.25	$54.30
Purchase #6	$225.83	10.333%	$249.165	$249.17	$249.15	$249.20
Purchase #7	$227.74	13.848%	$259.2774	$259.28	$259.30	$259.30
7 purchase totals =	$1,081.61		$1,211.2359	$1,211.23	$1,211.25	$1,211.30