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	$65.25	11.710%	$72.8908	$72.89	$72.90	$72.90
Purchase #2	$110.91	11.131%	$123.2554	$123.26	$123.25	$123.30
Purchase #3	$33.51	3.213%	$34.5867	$34.59	$34.60	$34.60
Purchase #4	$74.44	4.324%	$77.6588	$77.66	$77.65	$77.70
Purchase #5	$31.45	4.406%	$32.8357	$32.84	$32.85	$32.80
Purchase #6	$246.52	13.786%	$280.5052	$280.51	$280.50	$280.50
Purchase #7	$40.87	11.846%	$45.7115	$45.71	$45.70	$45.70
7 purchase totals =	$602.95		$667.4441	$667.46	$667.45	$667.50