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	$70.32	12.201%	$78.8997	$78.90	$78.90	$78.90
Purchase #2	$216.84	8.192%	$234.6035	$234.60	$234.60	$234.60
Purchase #3	$187.95	8.322%	$203.5912	$203.59	$203.60	$203.60
Purchase #4	$143.49	9.822%	$157.5836	$157.58	$157.60	$157.60
Purchase #5	$124.30	5.783%	$131.4883	$131.49	$131.50	$131.50
Purchase #6	$52.42	13.393%	$59.4406	$59.44	$59.45	$59.40
Purchase #7	$30.70	10.816%	$34.0205	$34.02	$34.00	$34.00
7 purchase totals =	$826.02		$899.6274	$899.62	$899.65	$899.60