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	$94.42	13.746%	$107.399	$107.40	$107.40	$107.40
Purchase #2	$228.85	3.703%	$237.3243	$237.32	$237.30	$237.30
Purchase #3	$114.65	10.714%	$126.9336	$126.93	$126.95	$126.90
Purchase #4	$116.52	9.708%	$127.8318	$127.83	$127.85	$127.80
Purchase #5	$59.44	12.493%	$66.8658	$66.87	$66.85	$66.90
Purchase #6	$184.45	6.309%	$196.087	$196.09	$196.10	$196.10
Purchase #7	$146.37	4.380%	$152.781	$152.78	$152.80	$152.80
7 purchase totals =	$944.70		$1,015.2225	$1,015.22	$1,015.25	$1,015.20