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	$136.83	13.866%	$155.8028	$155.80	$155.80	$155.80
Purchase #2	$128.92	6.340%	$137.0935	$137.09	$137.10	$137.10
Purchase #3	$161.61	5.210%	$170.0299	$170.03	$170.05	$170.00
Purchase #4	$60.59	5.505%	$63.9255	$63.93	$63.95	$63.90
Purchase #5	$187.58	6.765%	$200.2698	$200.27	$200.25	$200.30
Purchase #6	$84.30	7.606%	$90.7119	$90.71	$90.70	$90.70
Purchase #7	$247.60	3.284%	$255.7312	$255.73	$255.75	$255.70
7 purchase totals =	$1,007.43		$1,073.5646	$1,073.56	$1,073.60	$1,073.50