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	$29.65	6.334%	$31.528	$31.53	$31.55	$31.50
Purchase #2	$66.92	11.469%	$74.5951	$74.60	$74.60	$74.60
Purchase #3	$140.82	10.452%	$155.5385	$155.54	$155.55	$155.50
Purchase #4	$32.55	5.853%	$34.4552	$34.46	$34.45	$34.50
Purchase #5	$159.52	11.682%	$178.1551	$178.16	$178.15	$178.20
Purchase #6	$33.72	5.858%	$35.6953	$35.70	$35.70	$35.70
Purchase #7	$60.97	10.756%	$67.5279	$67.53	$67.55	$67.50
7 purchase totals =	$524.15		$577.4951	$577.52	$577.55	$577.50