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	$38.60	3.102%	$39.7974	$39.80	$39.80	$39.80
Purchase #2	$172.83	10.481%	$190.9443	$190.94	$190.95	$190.90
Purchase #3	$26.27	4.684%	$27.5005	$27.50	$27.50	$27.50
Purchase #4	$151.85	11.130%	$168.7509	$168.75	$168.75	$168.80
Purchase #5	$181.56	6.212%	$192.8385	$192.84	$192.85	$192.80
Purchase #6	$11.96	13.268%	$13.5469	$13.55	$13.55	$13.50
Purchase #7	$40.64	8.210%	$43.9765	$43.98	$44.00	$44.00
7 purchase totals =	$623.71		$677.3550	$677.36	$677.40	$677.30