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	$224.59	9.810%	$246.6223	$246.62	$246.60	$246.60
Purchase #2	$30.52	6.827%	$32.6036	$32.60	$32.60	$32.60
Purchase #3	$46.48	13.691%	$52.8436	$52.84	$52.85	$52.80
Purchase #4	$178.63	6.657%	$190.5214	$190.52	$190.50	$190.50
Purchase #5	$63.93	10.176%	$70.4355	$70.44	$70.45	$70.40
Purchase #6	$247.81	9.698%	$271.8426	$271.84	$271.85	$271.80
Purchase #7	$84.28	5.636%	$89.03	$89.03	$89.05	$89.00
7 purchase totals =	$876.24		$953.8990	$953.89	$953.90	$953.70