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	$237.43	7.647%	$255.5863	$255.59	$255.60	$255.60
Purchase #2	$189.83	5.580%	$200.4225	$200.42	$200.40	$200.40
Purchase #3	$190.52	5.667%	$201.3168	$201.32	$201.30	$201.30
Purchase #4	$190.42	9.244%	$208.0224	$208.02	$208.00	$208.00
Purchase #5	$29.62	6.233%	$31.4662	$31.47	$31.45	$31.50
Purchase #6	$213.74	3.211%	$220.6032	$220.60	$220.60	$220.60
Purchase #7	$195.86	13.394%	$222.0935	$222.09	$222.10	$222.10
7 purchase totals =	$1,247.42		$1,339.5109	$1,339.51	$1,339.45	$1,339.50