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	$228.91	13.402%	$259.5885	$259.59	$259.60	$259.60
Purchase #2	$143.82	10.479%	$158.8909	$158.89	$158.90	$158.90
Purchase #3	$158.95	12.379%	$178.6264	$178.63	$178.65	$178.60
Purchase #4	$65.83	10.358%	$72.6487	$72.65	$72.65	$72.60
Purchase #5	$219.53	9.493%	$240.37	$240.37	$240.35	$240.40
Purchase #6	$172.89	3.821%	$179.4961	$179.50	$179.50	$179.50
Purchase #7	$200.57	8.312%	$217.2414	$217.24	$217.25	$217.20
7 purchase totals =	$1,190.50		$1,306.8620	$1,306.87	$1,306.90	$1,306.80