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	$19.48	3.139%	$20.0915	$20.09	$20.10	$20.10
Purchase #2	$90.42	3.837%	$93.8894	$93.89	$93.90	$93.90
Purchase #3	$245.72	13.772%	$279.5606	$279.56	$279.55	$279.60
Purchase #4	$215.68	3.162%	$222.4998	$222.50	$222.50	$222.50
Purchase #5	$141.87	8.233%	$153.5502	$153.55	$153.55	$153.60
Purchase #6	$224.39	13.671%	$255.0664	$255.07	$255.05	$255.10
Purchase #7	$141.42	10.452%	$156.2012	$156.20	$156.20	$156.20
7 purchase totals =	$1,078.98		$1,180.8591	$1,180.86	$1,180.85	$1,181.00