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	$38.42	12.853%	$43.3581	$43.36	$43.35	$43.40
Purchase #2	$107.79	13.693%	$122.5497	$122.55	$122.55	$122.50
Purchase #3	$223.44	4.628%	$233.7808	$233.78	$233.80	$233.80
Purchase #4	$131.25	10.861%	$145.5051	$145.51	$145.50	$145.50
Purchase #5	$213.94	9.477%	$234.2151	$234.22	$234.20	$234.20
Purchase #6	$162.32	8.725%	$176.4824	$176.48	$176.50	$176.50
Purchase #7	$100.89	12.484%	$113.4851	$113.49	$113.50	$113.50
7 purchase totals =	$978.05		$1,069.3763	$1,069.39	$1,069.40	$1,069.40