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	$100.36	10.722%	$111.1206	$111.12	$111.10	$111.10
Purchase #2	$34.63	10.840%	$38.3839	$38.38	$38.40	$38.40
Purchase #3	$159.89	7.634%	$172.096	$172.10	$172.10	$172.10
Purchase #4	$85.97	10.582%	$95.0673	$95.07	$95.05	$95.10
Purchase #5	$137.44	8.535%	$149.1705	$149.17	$149.15	$149.20
Purchase #6	$172.76	13.828%	$196.6493	$196.65	$196.65	$196.60
Purchase #7	$112.72	10.724%	$124.8081	$124.81	$124.80	$124.80
7 purchase totals =	$803.77		$887.2957	$887.30	$887.25	$887.30