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	$143.77	8.731%	$156.3226	$156.32	$156.30	$156.30
Purchase #2	$176.43	3.796%	$183.1273	$183.13	$183.15	$183.10
Purchase #3	$79.45	7.730%	$85.5915	$85.59	$85.60	$85.60
Purchase #4	$205.77	6.861%	$219.8879	$219.89	$219.90	$219.90
Purchase #5	$41.76	6.443%	$44.4506	$44.45	$44.45	$44.50
Purchase #6	$176.88	7.792%	$190.6625	$190.66	$190.65	$190.70
Purchase #7	$69.94	10.780%	$77.4795	$77.48	$77.50	$77.50
7 purchase totals =	$894.00		$957.5219	$957.52	$957.55	$957.60