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	$39.57	7.568%	$42.5647	$42.56	$42.55	$42.60
Purchase #2	$95.57	9.633%	$104.7763	$104.78	$104.80	$104.80
Purchase #3	$37.94	12.410%	$42.6484	$42.65	$42.65	$42.60
Purchase #4	$182.54	4.471%	$190.7014	$190.70	$190.70	$190.70
Purchase #5	$12.62	8.348%	$13.6735	$13.67	$13.65	$13.70
Purchase #6	$153.60	9.283%	$167.8587	$167.86	$167.85	$167.90
Purchase #7	$43.45	9.242%	$47.4656	$47.47	$47.45	$47.50
7 purchase totals =	$565.29		$609.6886	$609.69	$609.65	$609.80