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	$66.35	9.263%	$72.496	$72.50	$72.50	$72.50
Purchase #2	$122.93	6.422%	$130.8246	$130.82	$130.80	$130.80
Purchase #3	$48.89	5.165%	$51.4152	$51.42	$51.40	$51.40
Purchase #4	$120.25	9.603%	$131.7976	$131.80	$131.80	$131.80
Purchase #5	$34.41	11.231%	$38.2746	$38.27	$38.25	$38.30
Purchase #6	$79.59	4.856%	$83.4549	$83.45	$83.45	$83.50
Purchase #7	$173.83	5.505%	$183.3993	$183.40	$183.40	$183.40
7 purchase totals =	$646.25		$691.6622	$691.66	$691.60	$691.70