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	$48.81	5.396%	$51.4438	$51.44	$51.45	$51.40
Purchase #2	$111.75	10.835%	$123.8581	$123.86	$123.85	$123.90
Purchase #3	$117.72	10.668%	$130.2784	$130.28	$130.30	$130.30
Purchase #4	$103.56	8.170%	$112.0209	$112.02	$112.00	$112.00
Purchase #5	$137.46	9.470%	$150.4775	$150.48	$150.50	$150.50
Purchase #6	$95.87	3.759%	$99.4738	$99.47	$99.45	$99.50
Purchase #7	$250.73	11.826%	$280.3813	$280.38	$280.40	$280.40
7 purchase totals =	$865.90		$947.9338	$947.93	$947.95	$948.00