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	$135.82	3.127%	$140.0671	$140.07	$140.05	$140.10
Purchase #2	$187.48	4.856%	$196.584	$196.58	$196.60	$196.60
Purchase #3	$213.42	3.284%	$220.4287	$220.43	$220.45	$220.40
Purchase #4	$64.29	12.656%	$72.4265	$72.43	$72.45	$72.40
Purchase #5	$135.59	4.490%	$141.678	$141.68	$141.70	$141.70
Purchase #6	$135.47	7.691%	$145.889	$145.89	$145.90	$145.90
Purchase #7	$64.57	9.722%	$70.8475	$70.85	$70.85	$70.80
7 purchase totals =	$936.64		$987.9208	$987.93	$988.00	$987.90