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	$239.99	6.664%	$255.9829	$255.98	$256.00	$256.00
Purchase #2	$86.30	13.467%	$97.922	$97.92	$97.90	$97.90
Purchase #3	$229.69	3.186%	$237.0079	$237.01	$237.00	$237.00
Purchase #4	$97.50	12.351%	$109.5422	$109.54	$109.55	$109.50
Purchase #5	$20.34	12.625%	$22.9079	$22.91	$22.90	$22.90
Purchase #6	$178.97	9.708%	$196.3444	$196.34	$196.35	$196.30
Purchase #7	$142.43	9.795%	$156.381	$156.38	$156.40	$156.40
7 purchase totals =	$995.22		$1,076.0883	$1,076.08	$1,076.10	$1,076.00