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	$40.85	3.285%	$42.1919	$42.19	$42.20	$42.20
Purchase #2	$195.45	11.364%	$217.6609	$217.66	$217.65	$217.70
Purchase #3	$84.50	4.748%	$88.5121	$88.51	$88.50	$88.50
Purchase #4	$27.34	13.863%	$31.1301	$31.13	$31.15	$31.10
Purchase #5	$249.94	9.181%	$272.887	$272.89	$272.90	$272.90
Purchase #6	$92.43	11.254%	$102.8321	$102.83	$102.85	$102.80
Purchase #7	$237.36	3.746%	$246.2515	$246.25	$246.25	$246.30
7 purchase totals =	$927.87		$1,001.4656	$1,001.46	$1,001.50	$1,001.50