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	$78.55	4.622%	$82.1806	$82.18	$82.20	$82.20
Purchase #2	$136.71	6.128%	$145.0876	$145.09	$145.10	$145.10
Purchase #3	$148.62	10.750%	$164.5967	$164.60	$164.60	$164.60
Purchase #4	$128.81	13.420%	$146.0963	$146.10	$146.10	$146.10
Purchase #5	$180.94	13.105%	$204.6522	$204.65	$204.65	$204.70
Purchase #6	$60.89	6.133%	$64.6244	$64.62	$64.60	$64.60
Purchase #7	$11.77	8.483%	$12.7684	$12.77	$12.75	$12.80
7 purchase totals =	$746.29		$820.0062	$820.01	$820.00	$820.10