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	$241.63	10.389%	$266.7329	$266.73	$266.75	$266.70
Purchase #2	$54.38	9.300%	$59.4373	$59.44	$59.45	$59.40
Purchase #3	$105.95	5.403%	$111.6745	$111.67	$111.65	$111.70
Purchase #4	$231.53	11.342%	$257.7901	$257.79	$257.80	$257.80
Purchase #5	$5.82	3.827%	$6.0427	$6.04	$6.05	$6.00
Purchase #6	$43.69	13.395%	$49.5423	$49.54	$49.55	$49.50
Purchase #7	$179.68	9.460%	$196.6777	$196.68	$196.70	$196.70
7 purchase totals =	$862.68		$947.8975	$947.89	$947.95	$947.80