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	$175.83	13.680%	$199.8835	$199.88	$199.90	$199.90
Purchase #2	$84.51	7.492%	$90.8415	$90.84	$90.85	$90.80
Purchase #3	$114.96	6.450%	$122.3749	$122.37	$122.35	$122.40
Purchase #4	$100.36	5.105%	$105.4834	$105.48	$105.50	$105.50
Purchase #5	$69.55	12.242%	$78.0643	$78.06	$78.05	$78.10
Purchase #6	$135.35	12.652%	$152.4745	$152.47	$152.45	$152.50
Purchase #7	$111.72	5.465%	$117.8255	$117.83	$117.85	$117.80
7 purchase totals =	$792.28		$866.9476	$866.93	$866.95	$867.00