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	$39.43	8.859%	$42.9231	$42.92	$42.90	$42.90
Purchase #2	$105.61	4.729%	$110.6043	$110.60	$110.60	$110.60
Purchase #3	$246.77	11.630%	$275.4694	$275.47	$275.45	$275.50
Purchase #4	$108.52	3.569%	$112.3931	$112.39	$112.40	$112.40
Purchase #5	$148.67	5.761%	$157.2349	$157.23	$157.25	$157.20
Purchase #6	$79.89	5.676%	$84.4246	$84.42	$84.40	$84.40
Purchase #7	$40.64	4.472%	$42.4574	$42.46	$42.45	$42.50
7 purchase totals =	$769.53		$825.5068	$825.49	$825.45	$825.50