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	$139.82	9.773%	$153.4846	$153.48	$153.50	$153.50
Purchase #2	$97.50	13.724%	$110.8809	$110.88	$110.90	$110.90
Purchase #3	$20.53	12.523%	$23.101	$23.10	$23.10	$23.10
Purchase #4	$110.87	11.792%	$123.9438	$123.94	$123.95	$123.90
Purchase #5	$211.32	10.360%	$233.2128	$233.21	$233.20	$233.20
Purchase #6	$140.74	11.451%	$156.8561	$156.86	$156.85	$156.90
Purchase #7	$34.60	10.105%	$38.0963	$38.10	$38.10	$38.10
7 purchase totals =	$755.38		$839.5755	$839.57	$839.60	$839.60