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	$106.37	10.468%	$117.5048	$117.50	$117.50	$117.50
Purchase #2	$128.35	12.857%	$144.852	$144.85	$144.85	$144.90
Purchase #3	$55.31	5.583%	$58.398	$58.40	$58.40	$58.40
Purchase #4	$144.96	5.260%	$152.5849	$152.58	$152.60	$152.60
Purchase #5	$39.61	9.731%	$43.4644	$43.46	$43.45	$43.50
Purchase #6	$9.94	10.249%	$10.9588	$10.96	$10.95	$11.00
Purchase #7	$38.96	8.308%	$42.1968	$42.20	$42.20	$42.20
7 purchase totals =	$523.50		$569.9597	$569.95	$569.95	$570.10