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	$75.76	6.621%	$80.7761	$80.78	$80.80	$80.80
Purchase #2	$138.83	12.616%	$156.3448	$156.34	$156.35	$156.30
Purchase #3	$102.38	6.541%	$109.0767	$109.08	$109.10	$109.10
Purchase #4	$132.78	8.599%	$144.1978	$144.20	$144.20	$144.20
Purchase #5	$234.47	6.593%	$249.9286	$249.93	$249.95	$249.90
Purchase #6	$134.89	11.783%	$150.7841	$150.78	$150.80	$150.80
Purchase #7	$108.25	13.142%	$122.4762	$122.48	$122.50	$122.50
7 purchase totals =	$927.36		$1,013.5843	$1,013.59	$1,013.70	$1,013.60