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	$61.92	13.802%	$70.4662	$70.47	$70.45	$70.50
Purchase #2	$132.61	8.843%	$144.3367	$144.34	$144.35	$144.30
Purchase #3	$41.59	4.550%	$43.4823	$43.48	$43.50	$43.50
Purchase #4	$90.82	11.777%	$101.5159	$101.52	$101.50	$101.50
Purchase #5	$175.55	9.378%	$192.0131	$192.01	$192.00	$192.00
Purchase #6	$214.95	5.787%	$227.3892	$227.39	$227.40	$227.40
Purchase #7	$48.46	11.497%	$54.0314	$54.03	$54.05	$54.00
7 purchase totals =	$765.90		$833.2348	$833.24	$833.25	$833.20