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	$56.33	6.301%	$59.8794	$59.88	$59.90	$59.90
Purchase #2	$55.49	9.255%	$60.6256	$60.63	$60.65	$60.60
Purchase #3	$137.86	11.196%	$153.2948	$153.29	$153.30	$153.30
Purchase #4	$42.89	11.387%	$47.7739	$47.77	$47.75	$47.80
Purchase #5	$10.65	4.479%	$11.127	$11.13	$11.15	$11.10
Purchase #6	$193.43	5.776%	$204.6025	$204.60	$204.60	$204.60
Purchase #7	$119.45	9.331%	$130.5959	$130.60	$130.60	$130.60
7 purchase totals =	$616.10		$667.8991	$667.90	$667.95	$667.90