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	$80.62	10.446%	$89.0416	$89.04	$89.05	$89.00
Purchase #2	$37.44	8.123%	$40.4813	$40.48	$40.50	$40.50
Purchase #3	$52.55	7.238%	$56.3536	$56.35	$56.35	$56.40
Purchase #4	$112.39	6.624%	$119.8347	$119.83	$119.85	$119.80
Purchase #5	$96.30	11.330%	$107.2108	$107.21	$107.20	$107.20
Purchase #6	$126.98	3.285%	$131.1513	$131.15	$131.15	$131.20
Purchase #7	$208.87	7.177%	$223.8606	$223.86	$223.85	$223.90
7 purchase totals =	$715.15		$767.9339	$767.92	$767.95	$768.00