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	$239.62	9.708%	$262.8823	$262.88	$262.90	$262.90
Purchase #2	$219.89	13.676%	$249.9622	$249.96	$249.95	$250.00
Purchase #3	$87.97	8.530%	$95.4738	$95.47	$95.45	$95.50
Purchase #4	$160.25	5.162%	$168.5221	$168.52	$168.50	$168.50
Purchase #5	$245.43	10.208%	$270.4835	$270.48	$270.50	$270.50
Purchase #6	$66.32	12.311%	$74.4847	$74.48	$74.50	$74.50
Purchase #7	$168.89	8.223%	$182.7778	$182.78	$182.80	$182.80
7 purchase totals =	$1,188.37		$1,304.5864	$1,304.57	$1,304.60	$1,304.70