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	$49.88	5.290%	$52.5187	$52.52	$52.50	$52.50
Purchase #2	$62.37	6.158%	$66.2107	$66.21	$66.20	$66.20
Purchase #3	$77.70	10.514%	$85.8694	$85.87	$85.85	$85.90
Purchase #4	$117.81	7.800%	$126.9992	$127.00	$127.00	$127.00
Purchase #5	$145.55	5.525%	$153.5916	$153.59	$153.60	$153.60
Purchase #6	$60.68	10.853%	$67.2656	$67.27	$67.25	$67.30
Purchase #7	$59.64	10.305%	$65.7859	$65.79	$65.80	$65.80
7 purchase totals =	$573.63		$618.2411	$618.25	$618.20	$618.30