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	$77.92	13.713%	$88.6052	$88.61	$88.60	$88.60
Purchase #2	$89.28	12.169%	$100.1445	$100.14	$100.15	$100.10
Purchase #3	$98.82	6.855%	$105.5941	$105.59	$105.60	$105.60
Purchase #4	$92.71	8.704%	$100.7795	$100.78	$100.80	$100.80
Purchase #5	$204.60	11.687%	$228.5116	$228.51	$228.50	$228.50
Purchase #6	$76.47	8.433%	$82.9187	$82.92	$82.90	$82.90
Purchase #7	$46.60	8.390%	$50.5097	$50.51	$50.50	$50.50
7 purchase totals =	$686.40		$757.0633	$757.06	$757.05	$757.00