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	$31.89	9.127%	$34.8006	$34.80	$34.80	$34.80
Purchase #2	$156.61	9.358%	$171.2656	$171.27	$171.25	$171.30
Purchase #3	$158.39	3.200%	$163.4585	$163.46	$163.45	$163.50
Purchase #4	$102.81	6.733%	$109.7322	$109.73	$109.75	$109.70
Purchase #5	$89.61	11.835%	$100.2153	$100.22	$100.20	$100.20
Purchase #6	$151.38	13.612%	$171.9858	$171.99	$172.00	$172.00
Purchase #7	$205.83	13.137%	$232.8699	$232.87	$232.85	$232.90
7 purchase totals =	$896.52		$984.3279	$984.34	$984.30	$984.40