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	$140.48	13.624%	$159.619	$159.62	$159.60	$159.60
Purchase #2	$157.35	10.488%	$173.8529	$173.85	$173.85	$173.90
Purchase #3	$163.79	13.263%	$185.5135	$185.51	$185.50	$185.50
Purchase #4	$56.37	6.609%	$60.0955	$60.10	$60.10	$60.10
Purchase #5	$58.76	12.408%	$66.0509	$66.05	$66.05	$66.10
Purchase #6	$106.36	7.605%	$114.4487	$114.45	$114.45	$114.40
Purchase #7	$107.93	3.161%	$111.3417	$111.34	$111.35	$111.30
7 purchase totals =	$791.04		$870.9222	$870.92	$870.90	$870.90