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	$54.58	10.816%	$60.4834	$60.48	$60.50	$60.50
Purchase #2	$96.25	4.579%	$100.6573	$100.66	$100.65	$100.70
Purchase #3	$232.98	9.525%	$255.1713	$255.17	$255.15	$255.20
Purchase #4	$205.90	12.411%	$231.4542	$231.45	$231.45	$231.50
Purchase #5	$30.52	11.182%	$33.9327	$33.93	$33.95	$33.90
Purchase #6	$95.69	6.175%	$101.5989	$101.60	$101.60	$101.60
Purchase #7	$16.30	11.331%	$18.147	$18.15	$18.15	$18.10
7 purchase totals =	$732.22		$801.4448	$801.44	$801.45	$801.50