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	$27.37	5.397%	$28.8472	$28.85	$28.85	$28.80
Purchase #2	$30.41	8.605%	$33.0268	$33.03	$33.05	$33.00
Purchase #3	$108.83	4.381%	$113.5978	$113.60	$113.60	$113.60
Purchase #4	$155.45	8.752%	$169.055	$169.06	$169.05	$169.10
Purchase #5	$115.89	11.217%	$128.8894	$128.89	$128.90	$128.90
Purchase #6	$151.29	10.345%	$166.941	$166.94	$166.95	$166.90
Purchase #7	$155.50	12.440%	$174.8442	$174.84	$174.85	$174.80
7 purchase totals =	$744.74		$815.2014	$815.21	$815.25	$815.10