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	$226.42	12.662%	$255.0893	$255.09	$255.10	$255.10
Purchase #2	$143.36	6.605%	$152.8289	$152.83	$152.85	$152.80
Purchase #3	$170.82	6.831%	$182.4887	$182.49	$182.50	$182.50
Purchase #4	$93.52	3.780%	$97.0551	$97.06	$97.05	$97.10
Purchase #5	$46.89	7.128%	$50.2323	$50.23	$50.25	$50.20
Purchase #6	$80.92	8.647%	$87.9172	$87.92	$87.90	$87.90
Purchase #7	$76.64	13.330%	$86.8561	$86.86	$86.85	$86.90
7 purchase totals =	$838.57		$912.4676	$912.48	$912.50	$912.50