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	$89.39	11.599%	$99.7583	$99.76	$99.75	$99.80
Purchase #2	$241.76	6.677%	$257.9023	$257.90	$257.90	$257.90
Purchase #3	$247.85	3.660%	$256.9213	$256.92	$256.90	$256.90
Purchase #4	$237.46	10.343%	$262.0205	$262.02	$262.00	$262.00
Purchase #5	$108.25	3.305%	$111.8277	$111.83	$111.85	$111.80
Purchase #6	$109.66	4.737%	$114.8546	$114.85	$114.85	$114.90
Purchase #7	$55.74	3.249%	$57.551	$57.55	$57.55	$57.60
7 purchase totals =	$1,090.11		$1,160.8357	$1,160.83	$1,160.80	$1,160.90