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	$70.97	8.257%	$76.83	$76.83	$76.85	$76.80
Purchase #2	$237.66	11.689%	$265.4401	$265.44	$265.45	$265.40
Purchase #3	$105.26	12.586%	$118.508	$118.51	$118.50	$118.50
Purchase #4	$223.89	9.811%	$245.8558	$245.86	$245.85	$245.90
Purchase #5	$44.88	10.296%	$49.5008	$49.50	$49.50	$49.50
Purchase #6	$134.74	6.748%	$143.8323	$143.83	$143.85	$143.80
Purchase #7	$54.76	9.466%	$59.9436	$59.94	$59.95	$59.90
7 purchase totals =	$872.16		$959.9106	$959.91	$959.95	$959.80