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	$42.63	13.429%	$48.3548	$48.35	$48.35	$48.40
Purchase #2	$94.77	10.633%	$104.8469	$104.85	$104.85	$104.80
Purchase #3	$128.47	7.309%	$137.8599	$137.86	$137.85	$137.90
Purchase #4	$111.46	10.523%	$123.1889	$123.19	$123.20	$123.20
Purchase #5	$159.86	7.479%	$171.8159	$171.82	$171.80	$171.80
Purchase #6	$203.67	11.729%	$227.5585	$227.56	$227.55	$227.60
Purchase #7	$75.89	7.237%	$81.3822	$81.38	$81.40	$81.40
7 purchase totals =	$816.75		$895.0071	$895.01	$895.00	$895.10