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	$99.71	12.149%	$111.8238	$111.82	$111.80	$111.80
Purchase #2	$74.60	12.534%	$83.9504	$83.95	$83.95	$84.00
Purchase #3	$154.51	4.421%	$161.3409	$161.34	$161.35	$161.30
Purchase #4	$112.52	10.397%	$124.2187	$124.22	$124.20	$124.20
Purchase #5	$30.79	6.262%	$32.7181	$32.72	$32.70	$32.70
Purchase #6	$166.94	4.249%	$174.0333	$174.03	$174.05	$174.00
Purchase #7	$165.76	13.472%	$188.0912	$188.09	$188.10	$188.10
7 purchase totals =	$804.83		$876.1764	$876.17	$876.15	$876.10