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	$9.55	4.104%	$9.9419	$9.94	$9.95	$9.90
Purchase #2	$141.46	13.710%	$160.8542	$160.85	$160.85	$160.90
Purchase #3	$48.52	6.659%	$51.7509	$51.75	$51.75	$51.80
Purchase #4	$137.28	11.348%	$152.8585	$152.86	$152.85	$152.90
Purchase #5	$103.46	12.172%	$116.0532	$116.05	$116.05	$116.10
Purchase #6	$184.66	3.171%	$190.5156	$190.52	$190.50	$190.50
Purchase #7	$231.87	12.376%	$260.5662	$260.57	$260.55	$260.60
7 purchase totals =	$856.80		$942.5405	$942.54	$942.50	$942.70