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	$235.97	12.161%	$264.6663	$264.67	$264.65	$264.70
Purchase #2	$108.76	13.577%	$123.5263	$123.53	$123.55	$123.50
Purchase #3	$82.40	9.536%	$90.2577	$90.26	$90.25	$90.30
Purchase #4	$102.68	10.461%	$113.4214	$113.42	$113.40	$113.40
Purchase #5	$210.62	8.288%	$228.0762	$228.08	$228.10	$228.10
Purchase #6	$36.66	3.419%	$37.9134	$37.91	$37.90	$37.90
Purchase #7	$75.57	8.622%	$82.0856	$82.09	$82.10	$82.10
7 purchase totals =	$852.66		$939.9469	$939.96	$939.95	$940.00