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	$113.77	9.669%	$124.7704	$124.77	$124.75	$124.80
Purchase #2	$57.46	3.583%	$59.5188	$59.52	$59.50	$59.50
Purchase #3	$10.32	10.460%	$11.3995	$11.40	$11.40	$11.40
Purchase #4	$50.34	4.149%	$52.4286	$52.43	$52.45	$52.40
Purchase #5	$230.49	13.682%	$262.0256	$262.03	$262.05	$262.00
Purchase #6	$117.37	9.815%	$128.8899	$128.89	$128.90	$128.90
Purchase #7	$117.65	12.233%	$132.0421	$132.04	$132.05	$132.00
7 purchase totals =	$697.40		$771.0749	$771.08	$771.10	$771.00