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	$248.81	12.752%	$280.5383	$280.54	$280.55	$280.50
Purchase #2	$78.38	10.248%	$86.4124	$86.41	$86.40	$86.40
Purchase #3	$92.55	8.733%	$100.6324	$100.63	$100.65	$100.60
Purchase #4	$163.47	11.838%	$182.8216	$182.82	$182.80	$182.80
Purchase #5	$117.29	11.174%	$130.396	$130.40	$130.40	$130.40
Purchase #6	$27.82	3.514%	$28.7976	$28.80	$28.80	$28.80
Purchase #7	$211.70	10.758%	$234.4747	$234.47	$234.45	$234.50
7 purchase totals =	$940.02		$1,044.0730	$1,044.07	$1,044.05	$1,044.00