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	$158.32	6.477%	$168.5744	$168.57	$168.55	$168.60
Purchase #2	$132.93	7.640%	$143.0859	$143.09	$143.10	$143.10
Purchase #3	$63.82	12.760%	$71.9634	$71.96	$71.95	$72.00
Purchase #4	$183.87	13.430%	$208.5637	$208.56	$208.55	$208.60
Purchase #5	$131.77	6.259%	$140.0175	$140.02	$140.00	$140.00
Purchase #6	$137.29	5.538%	$144.8931	$144.89	$144.90	$144.90
Purchase #7	$14.48	8.749%	$15.7469	$15.75	$15.75	$15.70
7 purchase totals =	$822.48		$892.8449	$892.84	$892.80	$892.90