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	$59.72	11.344%	$66.4946	$66.49	$66.50	$66.50
Purchase #2	$136.36	3.457%	$141.074	$141.07	$141.05	$141.10
Purchase #3	$10.93	5.407%	$11.521	$11.52	$11.50	$11.50
Purchase #4	$45.79	8.612%	$49.7334	$49.73	$49.75	$49.70
Purchase #5	$137.77	10.383%	$152.0747	$152.07	$152.05	$152.10
Purchase #6	$141.67	6.285%	$150.574	$150.57	$150.55	$150.60
Purchase #7	$227.39	12.334%	$255.4363	$255.44	$255.45	$255.40
7 purchase totals =	$759.63		$826.9080	$826.89	$826.85	$826.90