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	$82.31	8.239%	$89.0915	$89.09	$89.10	$89.10
Purchase #2	$38.89	5.626%	$41.078	$41.08	$41.10	$41.10
Purchase #3	$39.51	4.590%	$41.3235	$41.32	$41.30	$41.30
Purchase #4	$77.97	3.412%	$80.6303	$80.63	$80.65	$80.60
Purchase #5	$157.38	11.502%	$175.4818	$175.48	$175.50	$175.50
Purchase #6	$93.63	9.593%	$102.6119	$102.61	$102.60	$102.60
Purchase #7	$160.52	11.202%	$178.5015	$178.50	$178.50	$178.50
7 purchase totals =	$650.21		$708.7185	$708.71	$708.75	$708.70