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	$178.56	12.323%	$200.5639	$200.56	$200.55	$200.60
Purchase #2	$175.58	7.495%	$188.7397	$188.74	$188.75	$188.70
Purchase #3	$171.55	11.243%	$190.8374	$190.84	$190.85	$190.80
Purchase #4	$217.43	7.141%	$232.9567	$232.96	$232.95	$233.00
Purchase #5	$40.96	13.792%	$46.6092	$46.61	$46.60	$46.60
Purchase #6	$31.89	6.146%	$33.85	$33.85	$33.85	$33.90
Purchase #7	$69.66	10.217%	$76.7772	$76.78	$76.80	$76.80
7 purchase totals =	$885.63		$970.3341	$970.34	$970.35	$970.40