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	$31.66	5.748%	$33.4798	$33.48	$33.50	$33.50
Purchase #2	$46.58	11.186%	$51.7904	$51.79	$51.80	$51.80
Purchase #3	$6.94	4.284%	$7.2373	$7.24	$7.25	$7.20
Purchase #4	$114.83	8.299%	$124.3597	$124.36	$124.35	$124.40
Purchase #5	$126.72	8.575%	$137.5862	$137.59	$137.60	$137.60
Purchase #6	$51.62	6.670%	$55.0631	$55.06	$55.05	$55.10
Purchase #7	$132.85	7.169%	$142.374	$142.37	$142.35	$142.40
7 purchase totals =	$511.20		$551.8905	$551.89	$551.90	$552.00