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	$117.81	4.309%	$122.8864	$122.89	$122.90	$122.90
Purchase #2	$217.73	6.291%	$231.4274	$231.43	$231.45	$231.40
Purchase #3	$65.39	10.605%	$72.3246	$72.32	$72.30	$72.30
Purchase #4	$44.48	7.865%	$47.9784	$47.98	$48.00	$48.00
Purchase #5	$19.25	11.581%	$21.4793	$21.48	$21.50	$21.50
Purchase #6	$120.83	9.505%	$132.3149	$132.31	$132.30	$132.30
Purchase #7	$86.82	13.833%	$98.8298	$98.83	$98.85	$98.80
7 purchase totals =	$672.31		$727.2408	$727.24	$727.30	$727.20