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	$10.28	11.806%	$11.4937	$11.49	$11.50	$11.50
Purchase #2	$161.26	12.536%	$181.4756	$181.48	$181.50	$181.50
Purchase #3	$52.93	6.414%	$56.3249	$56.32	$56.30	$56.30
Purchase #4	$57.69	8.306%	$62.4817	$62.48	$62.50	$62.50
Purchase #5	$127.38	10.691%	$140.9982	$141.00	$141.00	$141.00
Purchase #6	$103.61	12.271%	$116.324	$116.32	$116.30	$116.30
Purchase #7	$10.43	3.384%	$10.783	$10.78	$10.80	$10.80
7 purchase totals =	$523.58		$579.8811	$579.87	$579.90	$579.90