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	$11.96	11.178%	$13.2969	$13.30	$13.30	$13.30
Purchase #2	$121.82	8.247%	$131.8665	$131.87	$131.85	$131.90
Purchase #3	$224.29	6.753%	$239.4363	$239.44	$239.45	$239.40
Purchase #4	$243.82	3.315%	$251.9026	$251.90	$251.90	$251.90
Purchase #5	$43.70	4.848%	$45.8186	$45.82	$45.80	$45.80
Purchase #6	$124.42	13.835%	$141.6335	$141.63	$141.65	$141.60
Purchase #7	$142.57	11.390%	$158.8087	$158.81	$158.80	$158.80
7 purchase totals =	$912.58		$982.7631	$982.77	$982.75	$982.70