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	$11.85	13.580%	$13.4592	$13.46	$13.45	$13.50
Purchase #2	$199.26	11.559%	$222.2925	$222.29	$222.30	$222.30
Purchase #3	$74.40	12.564%	$83.7476	$83.75	$83.75	$83.70
Purchase #4	$92.64	7.821%	$99.8854	$99.89	$99.90	$99.90
Purchase #5	$126.32	11.292%	$140.5841	$140.58	$140.60	$140.60
Purchase #6	$91.81	4.395%	$95.845	$95.85	$95.85	$95.80
Purchase #7	$100.27	5.188%	$105.472	$105.47	$105.45	$105.50
7 purchase totals =	$696.55		$761.2858	$761.29	$761.30	$761.30