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	$122.87	12.238%	$137.9068	$137.91	$137.90	$137.90
Purchase #2	$242.66	5.139%	$255.1303	$255.13	$255.15	$255.10
Purchase #3	$166.38	4.222%	$173.4046	$173.40	$173.40	$173.40
Purchase #4	$155.86	9.680%	$170.9472	$170.95	$170.95	$170.90
Purchase #5	$62.58	8.719%	$68.0364	$68.04	$68.05	$68.00
Purchase #6	$208.89	6.595%	$222.6663	$222.67	$222.65	$222.70
Purchase #7	$110.55	10.802%	$122.4916	$122.49	$122.50	$122.50
7 purchase totals =	$1,069.79		$1,150.5832	$1,150.59	$1,150.60	$1,150.50