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	$99.59	9.117%	$108.6696	$108.67	$108.65	$108.70
Purchase #2	$56.59	12.181%	$63.4832	$63.48	$63.50	$63.50
Purchase #3	$103.31	7.761%	$111.3279	$111.33	$111.35	$111.30
Purchase #4	$184.58	10.419%	$203.8114	$203.81	$203.80	$203.80
Purchase #5	$40.53	10.614%	$44.8319	$44.83	$44.85	$44.80
Purchase #6	$55.72	3.658%	$57.7582	$57.76	$57.75	$57.80
Purchase #7	$47.82	4.185%	$49.8213	$49.82	$49.80	$49.80
7 purchase totals =	$588.14		$639.7035	$639.70	$639.70	$639.70