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	$140.72	9.809%	$154.5232	$154.52	$154.50	$154.50
Purchase #2	$217.78	6.126%	$231.1212	$231.12	$231.10	$231.10
Purchase #3	$216.28	10.319%	$238.5979	$238.60	$238.60	$238.60
Purchase #4	$132.74	5.233%	$139.6863	$139.69	$139.70	$139.70
Purchase #5	$76.93	3.385%	$79.5341	$79.53	$79.55	$79.50
Purchase #6	$83.34	4.672%	$87.2336	$87.23	$87.25	$87.20
Purchase #7	$192.75	4.254%	$200.9496	$200.95	$200.95	$200.90
7 purchase totals =	$1,060.54		$1,131.6459	$1,131.64	$1,131.65	$1,131.50