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	$200.68	13.305%	$227.3805	$227.38	$227.40	$227.40
Purchase #2	$172.93	8.738%	$188.0406	$188.04	$188.05	$188.00
Purchase #3	$98.75	12.556%	$111.1491	$111.15	$111.15	$111.10
Purchase #4	$33.95	13.154%	$38.4158	$38.42	$38.40	$38.40
Purchase #5	$100.43	11.778%	$112.2586	$112.26	$112.25	$112.30
Purchase #6	$39.40	3.457%	$40.7621	$40.76	$40.75	$40.80
Purchase #7	$176.74	7.863%	$190.6371	$190.64	$190.65	$190.60
7 purchase totals =	$822.88		$908.6438	$908.65	$908.65	$908.60