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	$36.46	10.797%	$40.3966	$40.40	$40.40	$40.40
Purchase #2	$82.78	4.838%	$86.7849	$86.78	$86.80	$86.80
Purchase #3	$176.50	12.135%	$197.9183	$197.92	$197.90	$197.90
Purchase #4	$47.66	12.202%	$53.4755	$53.48	$53.50	$53.50
Purchase #5	$118.33	4.280%	$123.3945	$123.39	$123.40	$123.40
Purchase #6	$112.84	12.194%	$126.5997	$126.60	$126.60	$126.60
Purchase #7	$63.28	5.671%	$66.8686	$66.87	$66.85	$66.90
7 purchase totals =	$637.85		$695.4381	$695.44	$695.45	$695.50