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	$58.83	12.668%	$66.2826	$66.28	$66.30	$66.30
Purchase #2	$30.95	11.198%	$34.4158	$34.42	$34.40	$34.40
Purchase #3	$196.38	10.709%	$217.4103	$217.41	$217.40	$217.40
Purchase #4	$105.97	4.766%	$111.0205	$111.02	$111.00	$111.00
Purchase #5	$151.64	3.828%	$157.4448	$157.44	$157.45	$157.40
Purchase #6	$202.97	13.501%	$230.373	$230.37	$230.35	$230.40
Purchase #7	$177.42	10.627%	$196.2744	$196.27	$196.25	$196.30
7 purchase totals =	$924.16		$1,013.2214	$1,013.21	$1,013.15	$1,013.20