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	$132.85	5.333%	$139.9349	$139.93	$139.95	$139.90
Purchase #2	$56.94	6.114%	$60.4213	$60.42	$60.40	$60.40
Purchase #3	$215.78	7.326%	$231.588	$231.59	$231.60	$231.60
Purchase #4	$107.97	7.789%	$116.3798	$116.38	$116.40	$116.40
Purchase #5	$154.99	4.854%	$162.5132	$162.51	$162.50	$162.50
Purchase #6	$78.42	10.102%	$86.342	$86.34	$86.35	$86.30
Purchase #7	$95.93	9.508%	$105.051	$105.05	$105.05	$105.10
7 purchase totals =	$842.88		$902.2302	$902.22	$902.25	$902.20