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	$10.41	6.504%	$11.0871	$11.09	$11.10	$11.10
Purchase #2	$45.92	3.449%	$47.5038	$47.50	$47.50	$47.50
Purchase #3	$132.88	13.414%	$150.7045	$150.70	$150.70	$150.70
Purchase #4	$33.28	11.490%	$37.1039	$37.10	$37.10	$37.10
Purchase #5	$34.77	5.308%	$36.6156	$36.62	$36.60	$36.60
Purchase #6	$156.91	13.670%	$178.3596	$178.36	$178.35	$178.40
Purchase #7	$176.83	7.181%	$189.5282	$189.53	$189.55	$189.50
7 purchase totals =	$591.00		$650.9027	$650.90	$650.90	$650.90