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	$212.44	8.348%	$230.1745	$230.17	$230.15	$230.20
Purchase #2	$56.69	5.122%	$59.5937	$59.59	$59.60	$59.60
Purchase #3	$160.90	7.196%	$172.4784	$172.48	$172.50	$172.50
Purchase #4	$116.92	11.537%	$130.4091	$130.41	$130.40	$130.40
Purchase #5	$142.46	10.379%	$157.2459	$157.25	$157.25	$157.20
Purchase #6	$77.38	10.104%	$85.1985	$85.20	$85.20	$85.20
Purchase #7	$22.73	4.325%	$23.7131	$23.71	$23.70	$23.70
7 purchase totals =	$789.52		$858.8132	$858.81	$858.80	$858.80