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	$56.67	8.486%	$61.479	$61.48	$61.50	$61.50
Purchase #2	$85.87	4.680%	$89.8887	$89.89	$89.90	$89.90
Purchase #3	$18.67	10.548%	$20.6393	$20.64	$20.65	$20.60
Purchase #4	$230.74	10.128%	$254.1093	$254.11	$254.10	$254.10
Purchase #5	$67.87	5.758%	$71.778	$71.78	$71.80	$71.80
Purchase #6	$49.94	5.643%	$52.7581	$52.76	$52.75	$52.80
Purchase #7	$214.51	7.337%	$230.2486	$230.25	$230.25	$230.20
7 purchase totals =	$724.27		$780.9010	$780.91	$780.95	$780.90