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	$153.25	11.856%	$171.4193	$171.42	$171.40	$171.40
Purchase #2	$57.55	11.572%	$64.2097	$64.21	$64.20	$64.20
Purchase #3	$241.96	9.713%	$265.4616	$265.46	$265.45	$265.50
Purchase #4	$61.95	4.655%	$64.8338	$64.83	$64.85	$64.80
Purchase #5	$49.90	3.184%	$51.4888	$51.49	$51.50	$51.50
Purchase #6	$231.34	3.510%	$239.46	$239.46	$239.45	$239.50
Purchase #7	$160.38	8.809%	$174.5079	$174.51	$174.50	$174.50
7 purchase totals =	$956.33		$1,031.3811	$1,031.38	$1,031.35	$1,031.40