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	$76.27	5.550%	$80.503	$80.50	$80.50	$80.50
Purchase #2	$185.89	13.141%	$210.3178	$210.32	$210.30	$210.30
Purchase #3	$116.73	13.816%	$132.8574	$132.86	$132.85	$132.90
Purchase #4	$18.90	11.686%	$21.1087	$21.11	$21.10	$21.10
Purchase #5	$140.45	12.672%	$158.2478	$158.25	$158.25	$158.20
Purchase #6	$29.66	7.565%	$31.9038	$31.90	$31.90	$31.90
Purchase #7	$219.77	4.179%	$228.9542	$228.95	$228.95	$229.00
7 purchase totals =	$787.67		$863.8927	$863.89	$863.85	$863.90