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	$121.93	8.169%	$131.8905	$131.89	$131.90	$131.90
Purchase #2	$222.91	3.388%	$230.4622	$230.46	$230.45	$230.50
Purchase #3	$176.38	6.360%	$187.5978	$187.60	$187.60	$187.60
Purchase #4	$224.68	10.353%	$247.9411	$247.94	$247.95	$247.90
Purchase #5	$82.96	3.522%	$85.8819	$85.88	$85.90	$85.90
Purchase #6	$45.30	9.540%	$49.6216	$49.62	$49.60	$49.60
Purchase #7	$125.34	11.664%	$139.9597	$139.96	$139.95	$140.00
7 purchase totals =	$999.50		$1,073.3548	$1,073.35	$1,073.35	$1,073.40