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	$74.82	5.673%	$79.0645	$79.06	$79.05	$79.10
Purchase #2	$63.69	6.401%	$67.7668	$67.77	$67.75	$67.80
Purchase #3	$56.81	7.563%	$61.1065	$61.11	$61.10	$61.10
Purchase #4	$71.85	10.847%	$79.6436	$79.64	$79.65	$79.60
Purchase #5	$105.92	4.462%	$110.6462	$110.65	$110.65	$110.60
Purchase #6	$72.70	6.752%	$77.6087	$77.61	$77.60	$77.60
Purchase #7	$44.52	12.427%	$50.0525	$50.05	$50.05	$50.10
7 purchase totals =	$490.31		$525.8888	$525.89	$525.85	$525.90