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	$46.52	12.710%	$52.4327	$52.43	$52.45	$52.40
Purchase #2	$12.25	3.669%	$12.6995	$12.70	$12.70	$12.70
Purchase #3	$150.38	10.113%	$165.5879	$165.59	$165.60	$165.60
Purchase #4	$106.86	11.599%	$119.2547	$119.25	$119.25	$119.30
Purchase #5	$126.96	10.872%	$140.7631	$140.76	$140.75	$140.80
Purchase #6	$92.39	13.452%	$104.8183	$104.82	$104.80	$104.80
Purchase #7	$71.71	3.839%	$74.4629	$74.46	$74.45	$74.50
7 purchase totals =	$607.07		$670.0191	$670.01	$670.00	$670.10