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	$126.80	3.594%	$131.3572	$131.36	$131.35	$131.40
Purchase #2	$126.57	12.860%	$142.8469	$142.85	$142.85	$142.80
Purchase #3	$211.89	5.662%	$223.8872	$223.89	$223.90	$223.90
Purchase #4	$58.38	9.313%	$63.8169	$63.82	$63.80	$63.80
Purchase #5	$154.52	5.664%	$163.272	$163.27	$163.25	$163.30
Purchase #6	$48.96	7.762%	$52.7603	$52.76	$52.75	$52.80
Purchase #7	$76.77	6.853%	$82.031	$82.03	$82.05	$82.00
7 purchase totals =	$803.89		$859.9715	$859.98	$859.95	$860.00