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	$160.57	11.866%	$179.6232	$179.62	$179.60	$179.60
Purchase #2	$12.94	8.516%	$14.042	$14.04	$14.05	$14.00
Purchase #3	$19.29	12.460%	$21.6935	$21.69	$21.70	$21.70
Purchase #4	$54.60	12.720%	$61.5451	$61.55	$61.55	$61.50
Purchase #5	$250.76	11.717%	$280.1415	$280.14	$280.15	$280.10
Purchase #6	$46.37	13.339%	$52.5553	$52.56	$52.55	$52.60
Purchase #7	$203.42	4.769%	$213.1211	$213.12	$213.10	$213.10
7 purchase totals =	$747.95		$822.7217	$822.72	$822.70	$822.60