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	$108.64	6.830%	$116.0601	$116.06	$116.05	$116.10
Purchase #2	$74.95	4.824%	$78.5656	$78.57	$78.55	$78.60
Purchase #3	$25.70	13.767%	$29.2381	$29.24	$29.25	$29.20
Purchase #4	$93.72	12.360%	$105.3038	$105.30	$105.30	$105.30
Purchase #5	$126.83	4.468%	$132.4968	$132.50	$132.50	$132.50
Purchase #6	$84.47	4.617%	$88.37	$88.37	$88.35	$88.40
Purchase #7	$250.89	8.606%	$272.4816	$272.48	$272.50	$272.50
7 purchase totals =	$765.20		$822.5160	$822.52	$822.50	$822.60