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	$155.31	7.172%	$166.4488	$166.45	$166.45	$166.40
Purchase #2	$100.57	10.843%	$111.4748	$111.47	$111.45	$111.50
Purchase #3	$104.40	3.174%	$107.7137	$107.71	$107.70	$107.70
Purchase #4	$9.79	5.640%	$10.3422	$10.34	$10.35	$10.30
Purchase #5	$210.59	4.330%	$219.7085	$219.71	$219.70	$219.70
Purchase #6	$25.73	13.208%	$29.1284	$29.13	$29.15	$29.10
Purchase #7	$50.78	6.868%	$54.2676	$54.27	$54.25	$54.30
7 purchase totals =	$657.17		$699.0840	$699.08	$699.05	$699.00