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	$9.95	12.766%	$11.2202	$11.22	$11.20	$11.20
Purchase #2	$233.94	9.545%	$256.2696	$256.27	$256.25	$256.30
Purchase #3	$232.50	5.118%	$244.3994	$244.40	$244.40	$244.40
Purchase #4	$58.57	6.823%	$62.5662	$62.57	$62.55	$62.60
Purchase #5	$54.39	5.385%	$57.3189	$57.32	$57.30	$57.30
Purchase #6	$122.95	9.709%	$134.8872	$134.89	$134.90	$134.90
Purchase #7	$124.74	5.685%	$131.8315	$131.83	$131.85	$131.80
7 purchase totals =	$837.04		$898.4930	$898.50	$898.45	$898.50