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	$27.80	12.430%	$31.2555	$31.26	$31.25	$31.30
Purchase #2	$104.52	6.310%	$111.1152	$111.12	$111.10	$111.10
Purchase #3	$23.69	10.302%	$26.1305	$26.13	$26.15	$26.10
Purchase #4	$158.61	8.542%	$172.1585	$172.16	$172.15	$172.20
Purchase #5	$129.42	8.840%	$140.8607	$140.86	$140.85	$140.90
Purchase #6	$143.51	9.605%	$157.2941	$157.29	$157.30	$157.30
Purchase #7	$63.80	4.357%	$66.5798	$66.58	$66.60	$66.60
7 purchase totals =	$651.35		$705.3943	$705.40	$705.40	$705.50