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	$60.85	8.188%	$65.8324	$65.83	$65.85	$65.80
Purchase #2	$39.59	6.484%	$42.157	$42.16	$42.15	$42.20
Purchase #3	$9.59	10.194%	$10.5676	$10.57	$10.55	$10.60
Purchase #4	$126.64	10.216%	$139.5775	$139.58	$139.60	$139.60
Purchase #5	$142.37	12.807%	$160.6033	$160.60	$160.60	$160.60
Purchase #6	$81.61	13.237%	$92.4127	$92.41	$92.40	$92.40
Purchase #7	$157.99	9.615%	$173.1807	$173.18	$173.20	$173.20
7 purchase totals =	$618.64		$684.3312	$684.33	$684.35	$684.40