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	$72.86	10.795%	$80.7252	$80.73	$80.75	$80.70
Purchase #2	$93.48	12.162%	$104.849	$104.85	$104.85	$104.80
Purchase #3	$157.79	13.706%	$179.4167	$179.42	$179.40	$179.40
Purchase #4	$94.38	8.397%	$102.3051	$102.31	$102.30	$102.30
Purchase #5	$170.85	3.402%	$176.6623	$176.66	$176.65	$176.70
Purchase #6	$163.73	4.811%	$171.6071	$171.61	$171.60	$171.60
Purchase #7	$87.50	3.803%	$90.8276	$90.83	$90.85	$90.80
7 purchase totals =	$840.59		$906.3930	$906.41	$906.40	$906.30