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	$107.96	10.737%	$119.5517	$119.55	$119.55	$119.60
Purchase #2	$85.63	5.709%	$90.5186	$90.52	$90.50	$90.50
Purchase #3	$75.82	12.594%	$85.3688	$85.37	$85.35	$85.40
Purchase #4	$204.39	9.104%	$222.9977	$223.00	$223.00	$223.00
Purchase #5	$21.84	9.278%	$23.8663	$23.87	$23.85	$23.90
Purchase #6	$23.80	4.484%	$24.8672	$24.87	$24.85	$24.90
Purchase #7	$18.39	11.177%	$20.4455	$20.45	$20.45	$20.40
7 purchase totals =	$537.83		$587.6158	$587.63	$587.55	$587.70