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	$45.29	7.436%	$48.6578	$48.66	$48.65	$48.70
Purchase #2	$111.39	11.271%	$123.9448	$123.94	$123.95	$123.90
Purchase #3	$78.55	9.349%	$85.8936	$85.89	$85.90	$85.90
Purchase #4	$127.27	4.338%	$132.791	$132.79	$132.80	$132.80
Purchase #5	$175.80	13.794%	$200.0499	$200.05	$200.05	$200.00
Purchase #6	$134.91	8.493%	$146.3679	$146.37	$146.35	$146.40
Purchase #7	$64.82	8.325%	$70.2163	$70.22	$70.20	$70.20
7 purchase totals =	$738.03		$807.9213	$807.92	$807.90	$807.90