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	$69.45	13.182%	$78.6049	$78.60	$78.60	$78.60
Purchase #2	$141.27	6.796%	$150.8707	$150.87	$150.85	$150.90
Purchase #3	$126.43	13.178%	$143.0909	$143.09	$143.10	$143.10
Purchase #4	$129.87	11.317%	$144.5674	$144.57	$144.55	$144.60
Purchase #5	$248.68	12.703%	$280.2698	$280.27	$280.25	$280.30
Purchase #6	$151.25	6.320%	$160.809	$160.81	$160.80	$160.80
Purchase #7	$147.41	7.245%	$158.0899	$158.09	$158.10	$158.10
7 purchase totals =	$1,014.36		$1,116.3026	$1,116.30	$1,116.25	$1,116.40