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	$129.43	10.351%	$142.8273	$142.83	$142.85	$142.80
Purchase #2	$129.34	11.276%	$143.9244	$143.92	$143.90	$143.90
Purchase #3	$80.30	3.434%	$83.0575	$83.06	$83.05	$83.10
Purchase #4	$81.88	12.625%	$92.2174	$92.22	$92.20	$92.20
Purchase #5	$248.76	8.556%	$270.0439	$270.04	$270.05	$270.00
Purchase #6	$13.86	13.202%	$15.6898	$15.69	$15.70	$15.70
Purchase #7	$161.46	3.747%	$167.5099	$167.51	$167.50	$167.50
7 purchase totals =	$845.03		$915.2702	$915.27	$915.25	$915.20