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	$123.36	11.370%	$137.386	$137.39	$137.40	$137.40
Purchase #2	$214.32	13.794%	$243.8833	$243.88	$243.90	$243.90
Purchase #3	$80.53	12.234%	$90.382	$90.38	$90.40	$90.40
Purchase #4	$40.65	6.828%	$43.4256	$43.43	$43.45	$43.40
Purchase #5	$129.64	12.532%	$145.8865	$145.89	$145.90	$145.90
Purchase #6	$100.25	11.487%	$111.7657	$111.77	$111.75	$111.80
Purchase #7	$117.78	4.325%	$122.874	$122.87	$122.85	$122.90
7 purchase totals =	$806.53		$895.6031	$895.61	$895.65	$895.70