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	$54.47	10.596%	$60.2416	$60.24	$60.25	$60.20
Purchase #2	$203.74	11.717%	$227.6122	$227.61	$227.60	$227.60
Purchase #3	$129.47	5.393%	$136.4523	$136.45	$136.45	$136.50
Purchase #4	$244.88	11.338%	$272.6445	$272.64	$272.65	$272.60
Purchase #5	$126.50	10.345%	$139.5864	$139.59	$139.60	$139.60
Purchase #6	$82.48	9.451%	$90.2752	$90.28	$90.30	$90.30
Purchase #7	$33.61	3.547%	$34.8021	$34.80	$34.80	$34.80
7 purchase totals =	$875.15		$961.6143	$961.61	$961.65	$961.60