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	$38.78	4.360%	$40.4708	$40.47	$40.45	$40.50
Purchase #2	$248.30	10.510%	$274.3963	$274.40	$274.40	$274.40
Purchase #3	$215.98	13.671%	$245.5066	$245.51	$245.50	$245.50
Purchase #4	$87.64	12.212%	$98.3426	$98.34	$98.35	$98.30
Purchase #5	$239.99	13.179%	$271.6183	$271.62	$271.60	$271.60
Purchase #6	$35.47	10.567%	$39.2181	$39.22	$39.20	$39.20
Purchase #7	$51.55	9.472%	$56.4328	$56.43	$56.45	$56.40
7 purchase totals =	$917.71		$1,025.9855	$1,025.99	$1,025.95	$1,025.90