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	$6.90	11.830%	$7.7163	$7.72	$7.70	$7.70
Purchase #2	$85.53	13.389%	$96.9816	$96.98	$97.00	$97.00
Purchase #3	$11.76	6.129%	$12.4808	$12.48	$12.50	$12.50
Purchase #4	$64.81	4.177%	$67.5171	$67.52	$67.50	$67.50
Purchase #5	$231.45	11.427%	$257.8978	$257.90	$257.90	$257.90
Purchase #6	$227.59	12.847%	$256.8285	$256.83	$256.85	$256.80
Purchase #7	$150.90	4.301%	$157.3902	$157.39	$157.40	$157.40
7 purchase totals =	$778.94		$856.8123	$856.82	$856.85	$856.80