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	$225.48	10.826%	$249.8905	$249.89	$249.90	$249.90
Purchase #2	$60.27	3.733%	$62.5199	$62.52	$62.50	$62.50
Purchase #3	$133.99	12.564%	$150.8245	$150.82	$150.80	$150.80
Purchase #4	$209.76	6.114%	$222.5847	$222.58	$222.60	$222.60
Purchase #5	$119.46	13.567%	$135.6671	$135.67	$135.65	$135.70
Purchase #6	$32.69	7.571%	$35.165	$35.17	$35.15	$35.20
Purchase #7	$105.33	7.443%	$113.1697	$113.17	$113.15	$113.20
7 purchase totals =	$886.98		$969.8214	$969.82	$969.75	$969.90