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	$64.58	9.716%	$70.8546	$70.85	$70.85	$70.90
Purchase #2	$211.82	10.580%	$234.2306	$234.23	$234.25	$234.20
Purchase #3	$98.84	12.742%	$111.4342	$111.43	$111.45	$111.40
Purchase #4	$29.93	4.221%	$31.1933	$31.19	$31.20	$31.20
Purchase #5	$247.46	13.255%	$280.2608	$280.26	$280.25	$280.30
Purchase #6	$130.29	13.507%	$147.8883	$147.89	$147.90	$147.90
Purchase #7	$8.97	11.197%	$9.9744	$9.97	$9.95	$10.00
7 purchase totals =	$791.89		$885.8362	$885.82	$885.85	$885.90