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	$179.65	11.837%	$200.9152	$200.92	$200.90	$200.90
Purchase #2	$56.75	4.247%	$59.1602	$59.16	$59.15	$59.20
Purchase #3	$156.97	10.506%	$173.4613	$173.46	$173.45	$173.50
Purchase #4	$27.71	7.251%	$29.7193	$29.72	$29.70	$29.70
Purchase #5	$151.46	6.342%	$161.0656	$161.07	$161.05	$161.10
Purchase #6	$10.86	6.111%	$11.5237	$11.52	$11.50	$11.50
Purchase #7	$136.69	7.485%	$146.9212	$146.92	$146.90	$146.90
7 purchase totals =	$720.09		$782.7665	$782.77	$782.65	$782.80