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	$248.98	12.647%	$280.4685	$280.47	$280.45	$280.50
Purchase #2	$24.99	9.604%	$27.39	$27.39	$27.40	$27.40
Purchase #3	$87.63	4.379%	$91.4673	$91.47	$91.45	$91.50
Purchase #4	$11.37	9.380%	$12.4365	$12.44	$12.45	$12.40
Purchase #5	$217.78	10.523%	$240.697	$240.70	$240.70	$240.70
Purchase #6	$171.72	4.580%	$179.5848	$179.58	$179.60	$179.60
Purchase #7	$126.54	4.689%	$132.4735	$132.47	$132.45	$132.50
7 purchase totals =	$889.01		$964.5176	$964.52	$964.50	$964.60