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	$130.46	10.325%	$143.93	$143.93	$143.95	$143.90
Purchase #2	$178.32	6.593%	$190.0766	$190.08	$190.10	$190.10
Purchase #3	$11.59	10.446%	$12.8007	$12.80	$12.80	$12.80
Purchase #4	$169.77	8.161%	$183.6249	$183.62	$183.60	$183.60
Purchase #5	$150.26	11.851%	$168.0673	$168.07	$168.05	$168.10
Purchase #6	$80.44	12.102%	$90.1748	$90.17	$90.15	$90.20
Purchase #7	$20.38	12.127%	$22.8515	$22.85	$22.85	$22.90
7 purchase totals =	$741.22		$811.5258	$811.52	$811.50	$811.60