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	$38.52	11.330%	$42.8843	$42.88	$42.90	$42.90
Purchase #2	$105.52	13.198%	$119.4465	$119.45	$119.45	$119.40
Purchase #3	$87.75	3.152%	$90.5159	$90.52	$90.50	$90.50
Purchase #4	$156.29	10.477%	$172.6645	$172.66	$172.65	$172.70
Purchase #5	$46.57	3.828%	$48.3527	$48.35	$48.35	$48.40
Purchase #6	$10.76	10.188%	$11.8562	$11.86	$11.85	$11.90
Purchase #7	$138.77	6.586%	$147.9094	$147.91	$147.90	$147.90
7 purchase totals =	$584.18		$633.6295	$633.63	$633.60	$633.70