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	$38.27	13.680%	$43.5053	$43.51	$43.50	$43.50
Purchase #2	$116.90	9.119%	$127.5601	$127.56	$127.55	$127.60
Purchase #3	$208.32	11.606%	$232.4976	$232.50	$232.50	$232.50
Purchase #4	$12.98	5.650%	$13.7134	$13.71	$13.70	$13.70
Purchase #5	$17.52	5.509%	$18.4852	$18.49	$18.50	$18.50
Purchase #6	$93.65	4.583%	$97.942	$97.94	$97.95	$97.90
Purchase #7	$215.34	10.704%	$238.39	$238.39	$238.40	$238.40
7 purchase totals =	$702.98		$772.0936	$772.10	$772.10	$772.10