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	$72.61	12.165%	$81.443	$81.44	$81.45	$81.40
Purchase #2	$172.96	10.111%	$190.448	$190.45	$190.45	$190.40
Purchase #3	$52.50	8.462%	$56.9426	$56.94	$56.95	$56.90
Purchase #4	$7.49	6.498%	$7.9767	$7.98	$8.00	$8.00
Purchase #5	$87.75	13.400%	$99.5085	$99.51	$99.50	$99.50
Purchase #6	$126.35	4.846%	$132.4729	$132.47	$132.45	$132.50
Purchase #7	$190.96	7.781%	$205.8186	$205.82	$205.80	$205.80
7 purchase totals =	$710.62		$774.6103	$774.61	$774.60	$774.50