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	$82.42	7.522%	$88.6196	$88.62	$88.60	$88.60
Purchase #2	$170.78	11.503%	$190.4248	$190.42	$190.40	$190.40
Purchase #3	$88.55	10.353%	$97.7176	$97.72	$97.70	$97.70
Purchase #4	$115.29	11.716%	$128.7974	$128.80	$128.80	$128.80
Purchase #5	$222.69	8.242%	$241.0441	$241.04	$241.05	$241.00
Purchase #6	$142.72	6.406%	$151.8626	$151.86	$151.85	$151.90
Purchase #7	$168.29	13.186%	$190.4807	$190.48	$190.50	$190.50
7 purchase totals =	$990.74		$1,088.9468	$1,088.94	$1,088.90	$1,088.90