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	$25.54	13.855%	$29.0786	$29.08	$29.10	$29.10
Purchase #2	$155.89	5.214%	$164.0181	$164.02	$164.00	$164.00
Purchase #3	$196.85	6.111%	$208.8795	$208.88	$208.90	$208.90
Purchase #4	$30.69	3.580%	$31.7887	$31.79	$31.80	$31.80
Purchase #5	$154.78	11.393%	$172.4141	$172.41	$172.40	$172.40
Purchase #6	$197.83	4.301%	$206.3387	$206.34	$206.35	$206.30
Purchase #7	$89.41	10.647%	$98.9295	$98.93	$98.95	$98.90
7 purchase totals =	$850.99		$911.4472	$911.45	$911.50	$911.40