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	$226.82	12.838%	$255.9392	$255.94	$255.95	$255.90
Purchase #2	$184.31	11.516%	$205.5351	$205.54	$205.55	$205.50
Purchase #3	$178.39	7.638%	$192.0154	$192.02	$192.00	$192.00
Purchase #4	$127.74	10.800%	$141.5359	$141.54	$141.55	$141.50
Purchase #5	$205.96	5.440%	$217.1642	$217.16	$217.15	$217.20
Purchase #6	$158.96	10.412%	$175.5109	$175.51	$175.50	$175.50
Purchase #7	$64.90	11.667%	$72.4719	$72.47	$72.45	$72.50
7 purchase totals =	$1,147.08		$1,260.1726	$1,260.18	$1,260.15	$1,260.10