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	$49.93	8.623%	$54.2355	$54.24	$54.25	$54.20
Purchase #2	$18.90	9.638%	$20.7216	$20.72	$20.70	$20.70
Purchase #3	$126.29	11.376%	$140.6568	$140.66	$140.65	$140.70
Purchase #4	$106.38	11.273%	$118.3722	$118.37	$118.35	$118.40
Purchase #5	$117.47	3.270%	$121.3113	$121.31	$121.30	$121.30
Purchase #6	$43.53	3.579%	$45.0879	$45.09	$45.10	$45.10
Purchase #7	$156.31	7.177%	$167.5284	$167.53	$167.55	$167.50
7 purchase totals =	$618.81		$667.9137	$667.92	$667.90	$667.90