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	$248.75	12.778%	$280.5353	$280.54	$280.55	$280.50
Purchase #2	$25.27	4.346%	$26.3682	$26.37	$26.35	$26.40
Purchase #3	$112.55	3.588%	$116.5883	$116.59	$116.60	$116.60
Purchase #4	$176.45	13.589%	$200.4278	$200.43	$200.45	$200.40
Purchase #5	$34.28	3.640%	$35.5278	$35.53	$35.55	$35.50
Purchase #6	$113.59	4.514%	$118.7175	$118.72	$118.70	$118.70
Purchase #7	$109.80	5.509%	$115.8489	$115.85	$115.85	$115.80
7 purchase totals =	$820.69		$894.0138	$894.03	$894.05	$893.90