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	$19.38	9.536%	$21.2281	$21.23	$21.25	$21.20
Purchase #2	$38.55	5.629%	$40.72	$40.72	$40.70	$40.70
Purchase #3	$225.50	10.697%	$249.6217	$249.62	$249.60	$249.60
Purchase #4	$225.83	3.559%	$233.8673	$233.87	$233.85	$233.90
Purchase #5	$7.47	7.605%	$8.0381	$8.04	$8.05	$8.00
Purchase #6	$160.71	4.574%	$168.0609	$168.06	$168.05	$168.10
Purchase #7	$148.37	8.793%	$161.4162	$161.42	$161.40	$161.40
7 purchase totals =	$825.81		$882.9523	$882.96	$882.90	$882.90