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	$25.91	5.726%	$27.3936	$27.39	$27.40	$27.40
Purchase #2	$234.29	6.484%	$249.4814	$249.48	$249.50	$249.50
Purchase #3	$23.96	4.390%	$25.0118	$25.01	$25.00	$25.00
Purchase #4	$113.86	12.726%	$128.3498	$128.35	$128.35	$128.30
Purchase #5	$131.76	9.686%	$144.5223	$144.52	$144.50	$144.50
Purchase #6	$80.54	3.238%	$83.1479	$83.15	$83.15	$83.10
Purchase #7	$55.72	11.699%	$62.2387	$62.24	$62.25	$62.20
7 purchase totals =	$666.04		$720.1455	$720.14	$720.15	$720.00