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	$122.85	5.496%	$129.6018	$129.60	$129.60	$129.60
Purchase #2	$136.95	13.580%	$155.5478	$155.55	$155.55	$155.50
Purchase #3	$123.48	10.716%	$136.7121	$136.71	$136.70	$136.70
Purchase #4	$81.52	11.152%	$90.6111	$90.61	$90.60	$90.60
Purchase #5	$116.33	6.772%	$124.2079	$124.21	$124.20	$124.20
Purchase #6	$139.95	11.350%	$155.8343	$155.83	$155.85	$155.80
Purchase #7	$169.25	12.637%	$190.6381	$190.64	$190.65	$190.60
7 purchase totals =	$890.33		$983.1531	$983.15	$983.15	$983.00