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	$221.90	12.240%	$249.0606	$249.06	$249.05	$249.10
Purchase #2	$41.78	10.123%	$46.0094	$46.01	$46.00	$46.00
Purchase #3	$138.62	13.245%	$156.9802	$156.98	$157.00	$157.00
Purchase #4	$107.66	8.325%	$116.6227	$116.62	$116.60	$116.60
Purchase #5	$83.26	7.107%	$89.1773	$89.18	$89.20	$89.20
Purchase #6	$249.66	8.105%	$269.8949	$269.89	$269.90	$269.90
Purchase #7	$161.93	6.248%	$172.0474	$172.05	$172.05	$172.00
7 purchase totals =	$1,004.81		$1,099.7925	$1,099.79	$1,099.80	$1,099.80