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	$100.37	6.425%	$106.8188	$106.82	$106.80	$106.80
Purchase #2	$245.38	4.285%	$255.8945	$255.89	$255.90	$255.90
Purchase #3	$48.76	10.331%	$53.7974	$53.80	$53.80	$53.80
Purchase #4	$56.69	11.756%	$63.3545	$63.35	$63.35	$63.40
Purchase #5	$115.97	10.848%	$128.5504	$128.55	$128.55	$128.60
Purchase #6	$220.84	12.766%	$249.0324	$249.03	$249.05	$249.00
Purchase #7	$106.65	4.795%	$111.7639	$111.76	$111.75	$111.80
7 purchase totals =	$894.66		$969.2119	$969.20	$969.20	$969.30