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	$69.72	12.603%	$78.5068	$78.51	$78.50	$78.50
Purchase #2	$17.56	6.868%	$18.766	$18.77	$18.75	$18.80
Purchase #3	$33.64	6.517%	$35.8323	$35.83	$35.85	$35.80
Purchase #4	$124.47	11.239%	$138.4592	$138.46	$138.45	$138.50
Purchase #5	$37.82	10.287%	$41.7105	$41.71	$41.70	$41.70
Purchase #6	$51.77	4.782%	$54.2456	$54.25	$54.25	$54.20
Purchase #7	$77.36	12.578%	$87.0903	$87.09	$87.10	$87.10
7 purchase totals =	$412.34		$454.6107	$454.62	$454.60	$454.60