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	$50.67	6.377%	$53.9012	$53.90	$53.90	$53.90
Purchase #2	$166.39	3.730%	$172.5963	$172.60	$172.60	$172.60
Purchase #3	$150.84	3.252%	$155.7453	$155.75	$155.75	$155.70
Purchase #4	$21.39	8.377%	$23.1818	$23.18	$23.20	$23.20
Purchase #5	$197.77	12.316%	$222.1274	$222.13	$222.15	$222.10
Purchase #6	$81.31	13.642%	$92.4023	$92.40	$92.40	$92.40
Purchase #7	$76.87	6.822%	$82.1141	$82.11	$82.10	$82.10
7 purchase totals =	$745.24		$802.0684	$802.07	$802.10	$802.00