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	$148.65	4.193%	$154.8829	$154.88	$154.90	$154.90
Purchase #2	$106.99	7.113%	$114.6002	$114.60	$114.60	$114.60
Purchase #3	$54.42	9.228%	$59.4419	$59.44	$59.45	$59.40
Purchase #4	$163.52	8.161%	$176.8649	$176.86	$176.85	$176.90
Purchase #5	$181.96	4.157%	$189.5241	$189.52	$189.50	$189.50
Purchase #6	$46.25	8.250%	$50.0656	$50.07	$50.05	$50.10
Purchase #7	$208.58	12.472%	$234.5941	$234.59	$234.60	$234.60
7 purchase totals =	$910.37		$979.9737	$979.96	$979.95	$980.00