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	$112.77	8.713%	$122.5957	$122.60	$122.60	$122.60
Purchase #2	$106.33	13.773%	$120.9748	$120.97	$120.95	$121.00
Purchase #3	$198.34	12.465%	$223.0631	$223.06	$223.05	$223.10
Purchase #4	$58.85	6.644%	$62.76	$62.76	$62.75	$62.80
Purchase #5	$13.88	10.450%	$15.3305	$15.33	$15.35	$15.30
Purchase #6	$87.89	13.445%	$99.7068	$99.71	$99.70	$99.70
Purchase #7	$105.82	5.764%	$111.9195	$111.92	$111.90	$111.90
7 purchase totals =	$683.88		$756.3504	$756.35	$756.30	$756.40