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	$71.66	8.516%	$77.7626	$77.76	$77.75	$77.80
Purchase #2	$143.95	5.275%	$151.5434	$151.54	$151.55	$151.50
Purchase #3	$50.69	8.715%	$55.1076	$55.11	$55.10	$55.10
Purchase #4	$26.71	3.117%	$27.5426	$27.54	$27.55	$27.50
Purchase #5	$94.38	6.303%	$100.3288	$100.33	$100.35	$100.30
Purchase #6	$50.64	12.353%	$56.8956	$56.90	$56.90	$56.90
Purchase #7	$103.72	9.755%	$113.8379	$113.84	$113.85	$113.80
7 purchase totals =	$541.75		$583.0185	$583.02	$583.05	$582.90