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	$81.27	11.831%	$90.8851	$90.89	$90.90	$90.90
Purchase #2	$122.58	8.765%	$133.3241	$133.32	$133.30	$133.30
Purchase #3	$130.81	6.621%	$139.4709	$139.47	$139.45	$139.50
Purchase #4	$48.64	12.102%	$54.5264	$54.53	$54.55	$54.50
Purchase #5	$173.85	9.533%	$190.4231	$190.42	$190.40	$190.40
Purchase #6	$119.60	9.691%	$131.1904	$131.19	$131.20	$131.20
Purchase #7	$242.98	9.671%	$266.4786	$266.48	$266.50	$266.50
7 purchase totals =	$919.73		$1,006.2986	$1,006.30	$1,006.30	$1,006.30