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	$26.58	7.615%	$28.6041	$28.60	$28.60	$28.60
Purchase #2	$145.96	8.175%	$157.8922	$157.89	$157.90	$157.90
Purchase #3	$27.35	10.324%	$30.1736	$30.17	$30.15	$30.20
Purchase #4	$49.72	5.480%	$52.4447	$52.44	$52.45	$52.40
Purchase #5	$54.50	10.345%	$60.138	$60.14	$60.15	$60.10
Purchase #6	$100.88	10.510%	$111.4825	$111.48	$111.50	$111.50
Purchase #7	$63.60	10.130%	$70.0427	$70.04	$70.05	$70.00
7 purchase totals =	$468.59		$510.7778	$510.76	$510.80	$510.70