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	$72.89	11.255%	$81.0938	$81.09	$81.10	$81.10
Purchase #2	$232.82	9.212%	$254.2674	$254.27	$254.25	$254.30
Purchase #3	$43.95	4.472%	$45.9154	$45.92	$45.90	$45.90
Purchase #4	$113.62	11.424%	$126.5999	$126.60	$126.60	$126.60
Purchase #5	$100.90	11.375%	$112.3774	$112.38	$112.40	$112.40
Purchase #6	$172.45	8.665%	$187.3928	$187.39	$187.40	$187.40
Purchase #7	$100.47	11.672%	$112.1969	$112.20	$112.20	$112.20
7 purchase totals =	$837.10		$919.8436	$919.85	$919.85	$919.90