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	$15.85	3.739%	$16.4426	$16.44	$16.45	$16.40
Purchase #2	$128.71	7.163%	$137.9295	$137.93	$137.95	$137.90
Purchase #3	$118.72	9.149%	$129.5817	$129.58	$129.60	$129.60
Purchase #4	$240.93	5.257%	$253.5957	$253.60	$253.60	$253.60
Purchase #5	$56.25	5.555%	$59.3747	$59.37	$59.35	$59.40
Purchase #6	$244.65	4.304%	$255.1797	$255.18	$255.20	$255.20
Purchase #7	$157.78	5.257%	$166.0745	$166.07	$166.05	$166.10
7 purchase totals =	$962.89		$1,018.1784	$1,018.17	$1,018.20	$1,018.20