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	$139.40	11.162%	$154.9598	$154.96	$154.95	$155.00
Purchase #2	$107.93	8.113%	$116.6864	$116.69	$116.70	$116.70
Purchase #3	$105.93	10.802%	$117.3726	$117.37	$117.35	$117.40
Purchase #4	$54.32	10.371%	$59.9535	$59.95	$59.95	$60.00
Purchase #5	$19.64	5.388%	$20.6982	$20.70	$20.70	$20.70
Purchase #6	$154.90	6.493%	$164.9577	$164.96	$164.95	$165.00
Purchase #7	$215.73	4.491%	$225.4184	$225.42	$225.40	$225.40
7 purchase totals =	$797.85		$860.0466	$860.05	$860.00	$860.20