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	$128.69	3.125%	$132.7116	$132.71	$132.70	$132.70
Purchase #2	$152.55	12.433%	$171.5165	$171.52	$171.50	$171.50
Purchase #3	$81.40	11.266%	$90.5705	$90.57	$90.55	$90.60
Purchase #4	$126.37	8.191%	$136.721	$136.72	$136.70	$136.70
Purchase #5	$9.42	11.324%	$10.4867	$10.49	$10.50	$10.50
Purchase #6	$32.76	6.284%	$34.8186	$34.82	$34.80	$34.80
Purchase #7	$57.83	3.746%	$59.9963	$60.00	$60.00	$60.00
7 purchase totals =	$589.02		$636.8212	$636.83	$636.75	$636.80