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	$70.65	13.871%	$80.4499	$80.45	$80.45	$80.40
Purchase #2	$43.77	10.262%	$48.2617	$48.26	$48.25	$48.30
Purchase #3	$10.83	10.303%	$11.9458	$11.95	$11.95	$11.90
Purchase #4	$52.38	6.290%	$55.6747	$55.67	$55.65	$55.70
Purchase #5	$84.78	5.341%	$89.3081	$89.31	$89.30	$89.30
Purchase #6	$138.62	3.239%	$143.1099	$143.11	$143.10	$143.10
Purchase #7	$248.59	4.533%	$259.8586	$259.86	$259.85	$259.90
7 purchase totals =	$649.62		$688.6087	$688.61	$688.55	$688.60