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	$104.69	6.431%	$111.4226	$111.42	$111.40	$111.40
Purchase #2	$158.75	4.451%	$165.816	$165.82	$165.80	$165.80
Purchase #3	$33.66	12.212%	$37.7706	$37.77	$37.75	$37.80
Purchase #4	$219.72	4.660%	$229.959	$229.96	$229.95	$230.00
Purchase #5	$13.79	12.569%	$15.5233	$15.52	$15.50	$15.50
Purchase #6	$49.78	12.627%	$56.0657	$56.07	$56.05	$56.10
Purchase #7	$47.91	7.631%	$51.566	$51.57	$51.55	$51.60
7 purchase totals =	$628.30		$668.1232	$668.13	$668.00	$668.20