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	$39.59	3.407%	$40.9388	$40.94	$40.95	$40.90
Purchase #2	$126.71	8.648%	$137.6679	$137.67	$137.65	$137.70
Purchase #3	$177.70	7.709%	$191.3989	$191.40	$191.40	$191.40
Purchase #4	$105.42	6.326%	$112.0889	$112.09	$112.10	$112.10
Purchase #5	$94.47	5.491%	$99.6573	$99.66	$99.65	$99.70
Purchase #6	$93.33	6.681%	$99.5654	$99.57	$99.55	$99.60
Purchase #7	$90.52	7.420%	$97.2366	$97.24	$97.25	$97.20
7 purchase totals =	$727.74		$778.5538	$778.57	$778.55	$778.60