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	$46.87	3.476%	$48.4992	$48.50	$48.50	$48.50
Purchase #2	$165.27	12.616%	$186.1205	$186.12	$186.10	$186.10
Purchase #3	$155.66	13.166%	$176.1542	$176.15	$176.15	$176.20
Purchase #4	$45.50	13.330%	$51.5652	$51.57	$51.55	$51.60
Purchase #5	$127.83	12.315%	$143.5723	$143.57	$143.55	$143.60
Purchase #6	$83.77	10.864%	$92.8708	$92.87	$92.85	$92.90
Purchase #7	$90.70	7.813%	$97.7864	$97.79	$97.80	$97.80
7 purchase totals =	$715.60		$796.5686	$796.57	$796.50	$796.70