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	$28.41	11.107%	$31.5655	$31.57	$31.55	$31.60
Purchase #2	$103.83	4.560%	$108.5646	$108.56	$108.55	$108.60
Purchase #3	$108.49	9.168%	$118.4364	$118.44	$118.45	$118.40
Purchase #4	$162.81	9.874%	$178.8859	$178.89	$178.90	$178.90
Purchase #5	$217.66	11.196%	$242.0292	$242.03	$242.05	$242.00
Purchase #6	$241.99	13.174%	$273.8698	$273.87	$273.85	$273.90
Purchase #7	$168.87	10.189%	$186.0762	$186.08	$186.10	$186.10
7 purchase totals =	$1,032.06		$1,139.4276	$1,139.44	$1,139.45	$1,139.50