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	$28.94	12.644%	$32.5992	$32.60	$32.60	$32.60
Purchase #2	$137.64	4.210%	$143.4346	$143.43	$143.45	$143.40
Purchase #3	$160.29	6.465%	$170.6527	$170.65	$170.65	$170.70
Purchase #4	$169.31	13.265%	$191.769	$191.77	$191.75	$191.80
Purchase #5	$59.99	8.617%	$65.1593	$65.16	$65.15	$65.20
Purchase #6	$57.84	13.598%	$65.7051	$65.71	$65.70	$65.70
Purchase #7	$131.30	11.105%	$145.8809	$145.88	$145.90	$145.90
7 purchase totals =	$745.31		$815.2008	$815.20	$815.20	$815.30