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	$133.40	8.622%	$144.9017	$144.90	$144.90	$144.90
Purchase #2	$147.80	5.561%	$156.0192	$156.02	$156.00	$156.00
Purchase #3	$95.51	3.351%	$98.7105	$98.71	$98.70	$98.70
Purchase #4	$117.84	4.722%	$123.4044	$123.40	$123.40	$123.40
Purchase #5	$12.90	4.814%	$13.521	$13.52	$13.50	$13.50
Purchase #6	$41.51	5.317%	$43.7171	$43.72	$43.70	$43.70
Purchase #7	$77.98	12.687%	$87.8733	$87.87	$87.85	$87.90
7 purchase totals =	$626.94		$668.1472	$668.14	$668.05	$668.10