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	$171.43	8.158%	$185.4153	$185.42	$185.40	$185.40
Purchase #2	$222.42	5.182%	$233.9458	$233.95	$233.95	$233.90
Purchase #3	$123.89	4.502%	$129.4675	$129.47	$129.45	$129.50
Purchase #4	$135.82	5.325%	$143.0524	$143.05	$143.05	$143.10
Purchase #5	$74.29	11.595%	$82.9039	$82.90	$82.90	$82.90
Purchase #6	$30.62	8.476%	$33.2154	$33.22	$33.20	$33.20
Purchase #7	$111.43	12.742%	$125.6284	$125.63	$125.65	$125.60
7 purchase totals =	$869.90		$933.6287	$933.64	$933.60	$933.60