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	$21.80	10.254%	$24.0354	$24.04	$24.05	$24.00
Purchase #2	$95.52	5.497%	$100.7707	$100.77	$100.75	$100.80
Purchase #3	$99.34	12.608%	$111.8648	$111.86	$111.85	$111.90
Purchase #4	$199.66	12.439%	$224.4957	$224.50	$224.50	$224.50
Purchase #5	$192.81	10.359%	$212.7832	$212.78	$212.80	$212.80
Purchase #6	$42.72	9.248%	$46.6707	$46.67	$46.65	$46.70
Purchase #7	$237.35	12.273%	$266.48	$266.48	$266.50	$266.50
7 purchase totals =	$889.20		$987.1005	$987.10	$987.10	$987.20