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	$206.53	10.516%	$228.2487	$228.25	$228.25	$228.20
Purchase #2	$173.51	13.302%	$196.5903	$196.59	$196.60	$196.60
Purchase #3	$181.50	9.670%	$199.0511	$199.05	$199.05	$199.10
Purchase #4	$176.79	3.802%	$183.5116	$183.51	$183.50	$183.50
Purchase #5	$109.49	10.624%	$121.1222	$121.12	$121.10	$121.10
Purchase #6	$230.92	9.503%	$252.8643	$252.86	$252.85	$252.90
Purchase #7	$117.58	8.309%	$127.3497	$127.35	$127.35	$127.30
7 purchase totals =	$1,196.32		$1,308.7379	$1,308.73	$1,308.70	$1,308.70