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	$140.56	6.530%	$149.7386	$149.74	$149.75	$149.70
Purchase #2	$202.27	13.109%	$228.7856	$228.79	$228.80	$228.80
Purchase #3	$221.72	4.373%	$231.4158	$231.42	$231.40	$231.40
Purchase #4	$240.89	3.690%	$249.7788	$249.78	$249.80	$249.80
Purchase #5	$62.72	12.532%	$70.5801	$70.58	$70.60	$70.60
Purchase #6	$47.42	10.763%	$52.5238	$52.52	$52.50	$52.50
Purchase #7	$105.46	11.748%	$117.8494	$117.85	$117.85	$117.80
7 purchase totals =	$1,021.04		$1,100.6721	$1,100.68	$1,100.70	$1,100.60