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	$92.69	8.141%	$100.2359	$100.24	$100.25	$100.20
Purchase #2	$159.49	8.394%	$172.8776	$172.88	$172.90	$172.90
Purchase #3	$225.75	9.425%	$247.0269	$247.03	$247.05	$247.00
Purchase #4	$217.66	3.635%	$225.5719	$225.57	$225.55	$225.60
Purchase #5	$88.66	4.137%	$92.3279	$92.33	$92.35	$92.30
Purchase #6	$45.83	6.443%	$48.7828	$48.78	$48.80	$48.80
Purchase #7	$137.78	10.757%	$152.601	$152.60	$152.60	$152.60
7 purchase totals =	$967.86		$1,039.4240	$1,039.43	$1,039.50	$1,039.40