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	$93.77	6.131%	$99.519	$99.52	$99.50	$99.50
Purchase #2	$65.47	7.243%	$70.212	$70.21	$70.20	$70.20
Purchase #3	$90.33	4.739%	$94.6107	$94.61	$94.60	$94.60
Purchase #4	$194.72	12.249%	$218.5713	$218.57	$218.55	$218.60
Purchase #5	$55.80	12.709%	$62.8916	$62.89	$62.90	$62.90
Purchase #6	$48.50	8.573%	$52.6579	$52.66	$52.65	$52.70
Purchase #7	$70.26	8.791%	$76.4366	$76.44	$76.45	$76.40
7 purchase totals =	$618.85		$674.8991	$674.90	$674.85	$674.90