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	$38.81	10.298%	$42.8067	$42.81	$42.80	$42.80
Purchase #2	$193.63	8.386%	$209.8678	$209.87	$209.85	$209.90
Purchase #3	$83.72	5.792%	$88.5691	$88.57	$88.55	$88.60
Purchase #4	$247.33	9.401%	$270.5815	$270.58	$270.60	$270.60
Purchase #5	$71.26	12.560%	$80.2103	$80.21	$80.20	$80.20
Purchase #6	$48.35	11.700%	$54.007	$54.01	$54.00	$54.00
Purchase #7	$161.32	7.654%	$173.6674	$173.67	$173.65	$173.70
7 purchase totals =	$844.42		$919.7098	$919.72	$919.65	$919.80