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	$112.81	6.201%	$119.8053	$119.81	$119.80	$119.80
Purchase #2	$165.93	4.447%	$173.3089	$173.31	$173.30	$173.30
Purchase #3	$21.78	10.760%	$24.1235	$24.12	$24.10	$24.10
Purchase #4	$210.52	5.795%	$222.7196	$222.72	$222.70	$222.70
Purchase #5	$135.95	5.551%	$143.4966	$143.50	$143.50	$143.50
Purchase #6	$157.79	10.452%	$174.2822	$174.28	$174.30	$174.30
Purchase #7	$66.42	6.734%	$70.8927	$70.89	$70.90	$70.90
7 purchase totals =	$871.20		$928.6288	$928.63	$928.60	$928.60