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	$54.46	10.680%	$60.2763	$60.28	$60.30	$60.30
Purchase #2	$185.58	11.338%	$206.6211	$206.62	$206.60	$206.60
Purchase #3	$68.50	12.773%	$77.2495	$77.25	$77.25	$77.20
Purchase #4	$138.32	5.811%	$146.3578	$146.36	$146.35	$146.40
Purchase #5	$92.80	8.729%	$100.9005	$100.90	$100.90	$100.90
Purchase #6	$151.27	4.622%	$158.2617	$158.26	$158.25	$158.30
Purchase #7	$100.37	5.296%	$105.6856	$105.69	$105.70	$105.70
7 purchase totals =	$791.30		$855.3525	$855.36	$855.35	$855.40