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	$8.56	9.677%	$9.3884	$9.39	$9.40	$9.40
Purchase #2	$50.90	9.855%	$55.9162	$55.92	$55.90	$55.90
Purchase #3	$84.97	5.799%	$89.8974	$89.90	$89.90	$89.90
Purchase #4	$178.82	6.505%	$190.4522	$190.45	$190.45	$190.50
Purchase #5	$55.37	4.437%	$57.8268	$57.83	$57.85	$57.80
Purchase #6	$39.93	4.167%	$41.5939	$41.59	$41.60	$41.60
Purchase #7	$21.84	8.512%	$23.699	$23.70	$23.70	$23.70
7 purchase totals =	$440.39		$468.7739	$468.78	$468.80	$468.80