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	$137.85	12.387%	$154.9255	$154.93	$154.95	$154.90
Purchase #2	$107.31	12.667%	$120.903	$120.90	$120.90	$120.90
Purchase #3	$250.50	8.540%	$271.8927	$271.89	$271.90	$271.90
Purchase #4	$94.88	3.679%	$98.3706	$98.37	$98.35	$98.40
Purchase #5	$192.72	3.803%	$200.0491	$200.05	$200.05	$200.00
Purchase #6	$197.71	10.192%	$217.8606	$217.86	$217.85	$217.90
Purchase #7	$204.59	9.410%	$223.8419	$223.84	$223.85	$223.80
7 purchase totals =	$1,185.56		$1,287.8434	$1,287.84	$1,287.85	$1,287.80