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	$55.42	8.503%	$60.1324	$60.13	$60.15	$60.10
Purchase #2	$172.46	13.677%	$196.0474	$196.05	$196.05	$196.00
Purchase #3	$152.80	4.366%	$159.4712	$159.47	$159.45	$159.50
Purchase #4	$116.86	12.742%	$131.7503	$131.75	$131.75	$131.80
Purchase #5	$152.43	11.627%	$170.153	$170.15	$170.15	$170.20
Purchase #6	$181.50	8.492%	$196.913	$196.91	$196.90	$196.90
Purchase #7	$80.51	3.106%	$83.0106	$83.01	$83.00	$83.00
7 purchase totals =	$911.98		$997.4779	$997.47	$997.45	$997.50