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	$78.94	7.341%	$84.735	$84.74	$84.75	$84.70
Purchase #2	$233.34	10.523%	$257.8944	$257.89	$257.90	$257.90
Purchase #3	$90.68	10.627%	$100.3166	$100.32	$100.30	$100.30
Purchase #4	$19.29	8.120%	$20.8563	$20.86	$20.85	$20.90
Purchase #5	$133.57	8.395%	$144.7832	$144.78	$144.80	$144.80
Purchase #6	$93.59	5.628%	$98.8572	$98.86	$98.85	$98.90
Purchase #7	$107.50	4.174%	$111.9871	$111.99	$112.00	$112.00
7 purchase totals =	$756.91		$819.4298	$819.44	$819.45	$819.50