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	$94.49	6.470%	$100.6035	$100.60	$100.60	$100.60
Purchase #2	$82.91	8.613%	$90.051	$90.05	$90.05	$90.10
Purchase #3	$184.27	4.278%	$192.1531	$192.15	$192.15	$192.20
Purchase #4	$157.75	10.180%	$173.809	$173.81	$173.80	$173.80
Purchase #5	$94.77	9.540%	$103.8111	$103.81	$103.80	$103.80
Purchase #6	$40.76	3.548%	$42.2062	$42.21	$42.20	$42.20
Purchase #7	$185.73	12.337%	$208.6435	$208.64	$208.65	$208.60
7 purchase totals =	$840.68		$911.2774	$911.27	$911.25	$911.30