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	$99.51	6.605%	$106.0826	$106.08	$106.10	$106.10
Purchase #2	$52.58	3.480%	$54.4098	$54.41	$54.40	$54.40
Purchase #3	$146.72	4.861%	$153.8521	$153.85	$153.85	$153.90
Purchase #4	$59.96	3.537%	$62.0808	$62.08	$62.10	$62.10
Purchase #5	$139.39	6.244%	$148.0935	$148.09	$148.10	$148.10
Purchase #6	$48.72	4.472%	$50.8988	$50.90	$50.90	$50.90
Purchase #7	$210.62	8.638%	$228.8134	$228.81	$228.80	$228.80
7 purchase totals =	$757.50		$804.2310	$804.22	$804.25	$804.30