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	$121.72	12.149%	$136.5078	$136.51	$136.50	$136.50
Purchase #2	$48.96	5.567%	$51.6856	$51.69	$51.70	$51.70
Purchase #3	$172.26	13.811%	$196.0508	$196.05	$196.05	$196.10
Purchase #4	$131.92	5.700%	$139.4394	$139.44	$139.45	$139.40
Purchase #5	$159.85	6.289%	$169.903	$169.90	$169.90	$169.90
Purchase #6	$214.51	5.492%	$226.2909	$226.29	$226.30	$226.30
Purchase #7	$129.94	7.491%	$139.6738	$139.67	$139.65	$139.70
7 purchase totals =	$979.16		$1,059.5513	$1,059.55	$1,059.55	$1,059.60