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	$61.80	9.581%	$67.7211	$67.72	$67.70	$67.70
Purchase #2	$227.32	3.567%	$235.4285	$235.43	$235.45	$235.40
Purchase #3	$25.51	12.195%	$28.6209	$28.62	$28.60	$28.60
Purchase #4	$132.38	6.582%	$141.0933	$141.09	$141.10	$141.10
Purchase #5	$41.89	3.628%	$43.4098	$43.41	$43.40	$43.40
Purchase #6	$129.58	12.354%	$145.5883	$145.59	$145.60	$145.60
Purchase #7	$83.89	10.560%	$92.7488	$92.75	$92.75	$92.70
7 purchase totals =	$702.37		$754.6107	$754.61	$754.60	$754.50