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	$83.26	6.418%	$88.6036	$88.60	$88.60	$88.60
Purchase #2	$91.67	9.180%	$100.0853	$100.09	$100.10	$100.10
Purchase #3	$83.78	8.117%	$90.5804	$90.58	$90.60	$90.60
Purchase #4	$55.61	9.351%	$60.8101	$60.81	$60.80	$60.80
Purchase #5	$148.77	12.352%	$167.1461	$167.15	$167.15	$167.10
Purchase #6	$100.34	10.223%	$110.5978	$110.60	$110.60	$110.60
Purchase #7	$48.99	12.414%	$55.0716	$55.07	$55.05	$55.10
7 purchase totals =	$612.42		$672.8949	$672.90	$672.90	$672.90