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	$134.56	8.849%	$146.4672	$146.47	$146.45	$146.50
Purchase #2	$133.59	5.157%	$140.4792	$140.48	$140.50	$140.50
Purchase #3	$73.78	6.600%	$78.6495	$78.65	$78.65	$78.60
Purchase #4	$155.67	4.849%	$163.2184	$163.22	$163.20	$163.20
Purchase #5	$215.45	7.552%	$231.7208	$231.72	$231.70	$231.70
Purchase #6	$21.29	5.729%	$22.5097	$22.51	$22.50	$22.50
Purchase #7	$38.35	10.694%	$42.4511	$42.45	$42.45	$42.50
7 purchase totals =	$772.69		$825.4959	$825.50	$825.45	$825.50