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	$152.49	13.778%	$173.5001	$173.50	$173.50	$173.50
Purchase #2	$27.52	3.747%	$28.5512	$28.55	$28.55	$28.60
Purchase #3	$136.61	3.253%	$141.0539	$141.05	$141.05	$141.10
Purchase #4	$79.45	5.519%	$83.8348	$83.83	$83.85	$83.80
Purchase #5	$34.39	10.188%	$37.8937	$37.89	$37.90	$37.90
Purchase #6	$68.39	6.464%	$72.8107	$72.81	$72.80	$72.80
Purchase #7	$117.46	4.422%	$122.6541	$122.65	$122.65	$122.70
7 purchase totals =	$616.31		$660.2985	$660.28	$660.30	$660.40