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	$78.47	5.175%	$82.5308	$82.53	$82.55	$82.50
Purchase #2	$133.78	7.624%	$143.9794	$143.98	$144.00	$144.00
Purchase #3	$140.74	12.329%	$158.0918	$158.09	$158.10	$158.10
Purchase #4	$39.76	10.422%	$43.9038	$43.90	$43.90	$43.90
Purchase #5	$136.89	3.419%	$141.5703	$141.57	$141.55	$141.60
Purchase #6	$78.48	3.182%	$80.9772	$80.98	$81.00	$81.00
Purchase #7	$38.77	7.732%	$41.7677	$41.77	$41.75	$41.80
7 purchase totals =	$646.89		$692.8210	$692.82	$692.85	$692.90