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	$63.38	5.789%	$67.0491	$67.05	$67.05	$67.00
Purchase #2	$174.52	9.353%	$190.8429	$190.84	$190.85	$190.80
Purchase #3	$86.60	10.236%	$95.4644	$95.46	$95.45	$95.50
Purchase #4	$190.56	9.347%	$208.3716	$208.37	$208.35	$208.40
Purchase #5	$49.25	10.429%	$54.3863	$54.39	$54.40	$54.40
Purchase #6	$185.39	3.451%	$191.7878	$191.79	$191.80	$191.80
Purchase #7	$25.35	6.767%	$27.0654	$27.07	$27.05	$27.10
7 purchase totals =	$775.05		$834.9675	$834.97	$834.95	$835.00