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	$132.38	8.206%	$143.2431	$143.24	$143.25	$143.20
Purchase #2	$57.49	9.179%	$62.767	$62.77	$62.75	$62.80
Purchase #3	$94.49	6.703%	$100.8237	$100.82	$100.80	$100.80
Purchase #4	$81.59	6.684%	$87.0435	$87.04	$87.05	$87.00
Purchase #5	$63.81	3.358%	$65.9527	$65.95	$65.95	$66.00
Purchase #6	$157.76	9.452%	$172.6715	$172.67	$172.65	$172.70
Purchase #7	$156.51	8.215%	$169.3673	$169.37	$169.35	$169.40
7 purchase totals =	$744.03		$801.8688	$801.86	$801.80	$801.90