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	$242.52	11.684%	$270.856	$270.86	$270.85	$270.90
Purchase #2	$158.29	12.692%	$178.3802	$178.38	$178.40	$178.40
Purchase #3	$11.72	10.826%	$12.9888	$12.99	$13.00	$13.00
Purchase #4	$67.74	5.534%	$71.4887	$71.49	$71.50	$71.50
Purchase #5	$33.25	4.581%	$34.7732	$34.77	$34.75	$34.80
Purchase #6	$171.50	11.154%	$190.6291	$190.63	$190.65	$190.60
Purchase #7	$79.61	7.387%	$85.4908	$85.49	$85.50	$85.50
7 purchase totals =	$764.63		$844.6068	$844.61	$844.65	$844.70