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	$137.29	4.449%	$143.398	$143.40	$143.40	$143.40
Purchase #2	$43.86	11.813%	$49.0412	$49.04	$49.05	$49.00
Purchase #3	$41.35	12.534%	$46.5328	$46.53	$46.55	$46.50
Purchase #4	$105.67	11.679%	$118.0112	$118.01	$118.00	$118.00
Purchase #5	$143.39	8.675%	$155.8291	$155.83	$155.85	$155.80
Purchase #6	$131.49	7.131%	$140.8666	$140.87	$140.85	$140.90
Purchase #7	$248.80	12.598%	$280.1438	$280.14	$280.15	$280.10
7 purchase totals =	$851.85		$933.8227	$933.82	$933.85	$933.70