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	$71.42	9.800%	$78.4192	$78.42	$78.40	$78.40
Purchase #2	$247.66	13.387%	$280.8142	$280.81	$280.80	$280.80
Purchase #3	$108.97	11.612%	$121.6236	$121.62	$121.60	$121.60
Purchase #4	$101.69	8.614%	$110.4496	$110.45	$110.45	$110.40
Purchase #5	$182.46	6.349%	$194.0444	$194.04	$194.05	$194.00
Purchase #6	$40.56	3.776%	$42.0915	$42.09	$42.10	$42.10
Purchase #7	$90.76	11.873%	$101.5359	$101.54	$101.55	$101.50
7 purchase totals =	$843.52		$928.9784	$928.97	$928.95	$928.80