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	$58.52	3.256%	$60.4254	$60.43	$60.45	$60.40
Purchase #2	$133.98	12.186%	$150.3068	$150.31	$150.30	$150.30
Purchase #3	$105.63	5.631%	$111.578	$111.58	$111.60	$111.60
Purchase #4	$158.82	8.315%	$172.0259	$172.03	$172.05	$172.00
Purchase #5	$105.41	6.583%	$112.3491	$112.35	$112.35	$112.30
Purchase #6	$57.93	8.373%	$62.7805	$62.78	$62.80	$62.80
Purchase #7	$43.38	9.155%	$47.3514	$47.35	$47.35	$47.40
7 purchase totals =	$663.67		$716.8171	$716.83	$716.90	$716.80