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	$33.43	13.760%	$38.03	$38.03	$38.05	$38.00
Purchase #2	$122.52	9.661%	$134.3567	$134.36	$134.35	$134.40
Purchase #3	$21.49	8.171%	$23.2459	$23.25	$23.25	$23.20
Purchase #4	$51.55	7.846%	$55.5946	$55.59	$55.60	$55.60
Purchase #5	$176.87	4.227%	$184.3463	$184.35	$184.35	$184.30
Purchase #6	$143.89	12.271%	$161.5467	$161.55	$161.55	$161.50
Purchase #7	$104.90	6.314%	$111.5234	$111.52	$111.50	$111.50
7 purchase totals =	$654.65		$708.6436	$708.65	$708.65	$708.50