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	$172.78	8.556%	$187.5631	$187.56	$187.55	$187.60
Purchase #2	$126.90	4.534%	$132.6536	$132.65	$132.65	$132.70
Purchase #3	$176.30	13.579%	$200.2398	$200.24	$200.25	$200.20
Purchase #4	$184.50	3.237%	$190.4723	$190.47	$190.45	$190.50
Purchase #5	$124.84	12.161%	$140.0218	$140.02	$140.00	$140.00
Purchase #6	$190.62	9.390%	$208.5192	$208.52	$208.50	$208.50
Purchase #7	$146.56	6.473%	$156.0468	$156.05	$156.05	$156.00
7 purchase totals =	$1,122.50		$1,215.5166	$1,215.51	$1,215.45	$1,215.50