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	$49.69	8.777%	$54.0513	$54.05	$54.05	$54.10
Purchase #2	$92.27	10.589%	$102.0405	$102.04	$102.05	$102.00
Purchase #3	$69.53	4.738%	$72.8243	$72.82	$72.80	$72.80
Purchase #4	$115.54	12.845%	$130.3811	$130.38	$130.40	$130.40
Purchase #5	$247.25	13.426%	$280.4458	$280.45	$280.45	$280.40
Purchase #6	$20.58	13.312%	$23.3196	$23.32	$23.30	$23.30
Purchase #7	$155.77	9.485%	$170.5448	$170.54	$170.55	$170.50
7 purchase totals =	$750.63		$833.6074	$833.60	$833.60	$833.50