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	$86.45	5.188%	$90.935	$90.94	$90.95	$90.90
Purchase #2	$137.75	5.458%	$145.2684	$145.27	$145.25	$145.30
Purchase #3	$38.38	3.688%	$39.7955	$39.80	$39.80	$39.80
Purchase #4	$176.61	10.149%	$194.5341	$194.53	$194.55	$194.50
Purchase #5	$225.61	13.716%	$256.5547	$256.55	$256.55	$256.60
Purchase #6	$94.73	10.727%	$104.8917	$104.89	$104.90	$104.90
Purchase #7	$225.38	13.407%	$255.5967	$255.60	$255.60	$255.60
7 purchase totals =	$984.91		$1,087.5761	$1,087.58	$1,087.60	$1,087.60