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	$57.68	3.379%	$59.629	$59.63	$59.65	$59.60
Purchase #2	$122.89	4.261%	$128.1263	$128.13	$128.15	$128.10
Purchase #3	$65.83	8.625%	$71.5078	$71.51	$71.50	$71.50
Purchase #4	$190.47	9.103%	$207.8085	$207.81	$207.80	$207.80
Purchase #5	$45.64	4.334%	$47.618	$47.62	$47.60	$47.60
Purchase #6	$108.81	5.758%	$115.0753	$115.08	$115.10	$115.10
Purchase #7	$10.72	6.179%	$11.3824	$11.38	$11.40	$11.40
7 purchase totals =	$602.04		$641.1473	$641.16	$641.20	$641.10