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	$49.68	4.862%	$52.0954	$52.10	$52.10	$52.10
Purchase #2	$72.39	6.240%	$76.9071	$76.91	$76.90	$76.90
Purchase #3	$53.29	7.208%	$57.1311	$57.13	$57.15	$57.10
Purchase #4	$100.69	10.662%	$111.4256	$111.43	$111.45	$111.40
Purchase #5	$68.67	5.420%	$72.3919	$72.39	$72.40	$72.40
Purchase #6	$122.46	11.795%	$136.9042	$136.90	$136.90	$136.90
Purchase #7	$149.66	7.837%	$161.3889	$161.39	$161.40	$161.40
7 purchase totals =	$616.84		$668.2442	$668.25	$668.30	$668.20