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	$69.65	3.182%	$71.8663	$71.87	$71.85	$71.90
Purchase #2	$140.25	7.274%	$150.4518	$150.45	$150.45	$150.50
Purchase #3	$131.88	9.808%	$144.8148	$144.81	$144.80	$144.80
Purchase #4	$86.56	12.558%	$97.4302	$97.43	$97.45	$97.40
Purchase #5	$222.58	7.395%	$239.0398	$239.04	$239.05	$239.00
Purchase #6	$102.61	13.357%	$116.3156	$116.32	$116.30	$116.30
Purchase #7	$77.94	3.439%	$80.6204	$80.62	$80.60	$80.60
7 purchase totals =	$831.47		$900.5389	$900.54	$900.50	$900.50