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	$112.72	5.433%	$118.8441	$118.84	$118.85	$118.80
Purchase #2	$171.80	5.148%	$180.6443	$180.64	$180.65	$180.60
Purchase #3	$15.65	10.339%	$17.2681	$17.27	$17.25	$17.30
Purchase #4	$67.33	7.851%	$72.6161	$72.62	$72.60	$72.60
Purchase #5	$102.68	8.145%	$111.0433	$111.04	$111.05	$111.00
Purchase #6	$199.59	9.509%	$218.569	$218.57	$218.55	$218.60
Purchase #7	$240.98	12.797%	$271.8182	$271.82	$271.80	$271.80
7 purchase totals =	$910.75		$990.8031	$990.80	$990.75	$990.70