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	$99.79	5.325%	$105.1038	$105.10	$105.10	$105.10
Purchase #2	$141.98	13.724%	$161.4653	$161.47	$161.45	$161.50
Purchase #3	$212.73	11.174%	$236.5005	$236.50	$236.50	$236.50
Purchase #4	$56.54	11.251%	$62.9013	$62.90	$62.90	$62.90
Purchase #5	$14.85	6.446%	$15.8072	$15.81	$15.80	$15.80
Purchase #6	$176.90	3.140%	$182.4547	$182.45	$182.45	$182.50
Purchase #7	$133.94	6.733%	$142.9582	$142.96	$142.95	$143.00
7 purchase totals =	$836.73		$907.1910	$907.19	$907.15	$907.30