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	$137.79	4.145%	$143.5014	$143.50	$143.50	$143.50
Purchase #2	$13.48	10.628%	$14.9127	$14.91	$14.90	$14.90
Purchase #3	$145.82	9.723%	$159.9981	$160.00	$160.00	$160.00
Purchase #4	$92.40	10.874%	$102.4476	$102.45	$102.45	$102.40
Purchase #5	$177.84	10.534%	$196.5737	$196.57	$196.55	$196.60
Purchase #6	$76.78	9.459%	$84.0426	$84.04	$84.05	$84.00
Purchase #7	$40.49	5.785%	$42.8323	$42.83	$42.85	$42.80
7 purchase totals =	$684.60		$744.3084	$744.30	$744.30	$744.20