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	$40.77	4.698%	$42.6854	$42.69	$42.70	$42.70
Purchase #2	$50.51	4.142%	$52.6021	$52.60	$52.60	$52.60
Purchase #3	$180.27	11.412%	$200.8424	$200.84	$200.85	$200.80
Purchase #4	$155.55	5.135%	$163.5375	$163.54	$163.55	$163.50
Purchase #5	$116.81	13.675%	$132.7838	$132.78	$132.80	$132.80
Purchase #6	$23.40	3.720%	$24.2705	$24.27	$24.25	$24.30
Purchase #7	$66.72	9.213%	$72.8669	$72.87	$72.85	$72.90
7 purchase totals =	$634.03		$689.5886	$689.59	$689.60	$689.60