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	$222.73	7.726%	$239.9381	$239.94	$239.95	$239.90
Purchase #2	$149.68	12.839%	$168.8974	$168.90	$168.90	$168.90
Purchase #3	$217.47	8.402%	$235.7418	$235.74	$235.75	$235.70
Purchase #4	$18.27	3.395%	$18.8903	$18.89	$18.90	$18.90
Purchase #5	$57.97	5.222%	$60.9972	$61.00	$61.00	$61.00
Purchase #6	$160.44	9.833%	$176.2161	$176.22	$176.20	$176.20
Purchase #7	$80.88	12.389%	$90.9002	$90.90	$90.90	$90.90
7 purchase totals =	$907.44		$991.5811	$991.59	$991.60	$991.50