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	$23.96	10.393%	$26.4502	$26.45	$26.45	$26.50
Purchase #2	$195.27	8.307%	$211.4911	$211.49	$211.50	$211.50
Purchase #3	$235.33	10.243%	$259.4349	$259.43	$259.45	$259.40
Purchase #4	$103.67	12.380%	$116.5043	$116.50	$116.50	$116.50
Purchase #5	$145.56	9.560%	$159.4755	$159.48	$159.50	$159.50
Purchase #6	$132.70	13.171%	$150.1779	$150.18	$150.20	$150.20
Purchase #7	$129.69	7.636%	$139.5931	$139.59	$139.60	$139.60
7 purchase totals =	$966.18		$1,063.1270	$1,063.12	$1,063.20	$1,063.20