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	$151.32	8.493%	$164.1716	$164.17	$164.15	$164.20
Purchase #2	$61.32	6.149%	$65.0906	$65.09	$65.10	$65.10
Purchase #3	$157.87	13.678%	$179.4635	$179.46	$179.45	$179.50
Purchase #4	$57.92	13.227%	$65.5811	$65.58	$65.60	$65.60
Purchase #5	$152.49	10.805%	$168.9665	$168.97	$168.95	$169.00
Purchase #6	$112.70	4.510%	$117.7828	$117.78	$117.80	$117.80
Purchase #7	$112.78	3.564%	$116.7995	$116.80	$116.80	$116.80
7 purchase totals =	$806.40		$877.8556	$877.85	$877.85	$878.00