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	$102.55	8.743%	$111.5159	$111.52	$111.50	$111.50
Purchase #2	$76.82	7.451%	$82.5439	$82.54	$82.55	$82.50
Purchase #3	$126.71	9.273%	$138.4598	$138.46	$138.45	$138.50
Purchase #4	$224.99	10.170%	$247.8715	$247.87	$247.85	$247.90
Purchase #5	$39.48	5.654%	$41.7122	$41.71	$41.70	$41.70
Purchase #6	$83.99	6.644%	$89.5703	$89.57	$89.55	$89.60
Purchase #7	$151.42	4.736%	$158.5913	$158.59	$158.60	$158.60
7 purchase totals =	$805.96		$870.2649	$870.26	$870.20	$870.30