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	$72.87	7.132%	$78.0671	$78.07	$78.05	$78.10
Purchase #2	$50.81	3.866%	$52.7743	$52.77	$52.75	$52.80
Purchase #3	$212.94	4.526%	$222.5777	$222.58	$222.60	$222.60
Purchase #4	$21.98	13.502%	$24.9477	$24.95	$24.95	$24.90
Purchase #5	$111.46	7.105%	$119.3792	$119.38	$119.40	$119.40
Purchase #6	$18.91	3.724%	$19.6142	$19.61	$19.60	$19.60
Purchase #7	$160.37	9.345%	$175.3566	$175.36	$175.35	$175.40
7 purchase totals =	$649.34		$692.7168	$692.72	$692.70	$692.80