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	$241.69	12.161%	$271.0819	$271.08	$271.10	$271.10
Purchase #2	$179.25	3.473%	$185.4754	$185.48	$185.50	$185.50
Purchase #3	$67.95	7.212%	$72.8506	$72.85	$72.85	$72.90
Purchase #4	$112.48	4.863%	$117.9499	$117.95	$117.95	$117.90
Purchase #5	$132.55	4.736%	$138.8276	$138.83	$138.85	$138.80
Purchase #6	$51.53	13.395%	$58.4324	$58.43	$58.45	$58.40
Purchase #7	$228.77	13.144%	$258.8395	$258.84	$258.85	$258.80
7 purchase totals =	$1,014.22		$1,103.4573	$1,103.46	$1,103.55	$1,103.40