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	$55.34	3.389%	$57.2155	$57.22	$57.20	$57.20
Purchase #2	$33.90	8.821%	$36.8903	$36.89	$36.90	$36.90
Purchase #3	$72.28	10.227%	$79.6721	$79.67	$79.65	$79.70
Purchase #4	$99.48	6.422%	$105.8686	$105.87	$105.85	$105.90
Purchase #5	$148.86	13.531%	$169.0022	$169.00	$169.00	$169.00
Purchase #6	$159.86	11.750%	$178.6436	$178.64	$178.65	$178.60
Purchase #7	$53.94	4.431%	$56.3301	$56.33	$56.35	$56.30
7 purchase totals =	$623.66		$683.6224	$683.62	$683.60	$683.60