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	$225.83	13.581%	$256.5	$256.50	$256.50	$256.50
Purchase #2	$172.61	13.866%	$196.5441	$196.54	$196.55	$196.50
Purchase #3	$127.65	11.499%	$142.3285	$142.33	$142.35	$142.30
Purchase #4	$30.47	8.293%	$32.9969	$33.00	$33.00	$33.00
Purchase #5	$144.29	12.231%	$161.9381	$161.94	$161.95	$161.90
Purchase #6	$49.88	9.493%	$54.6151	$54.62	$54.60	$54.60
Purchase #7	$63.67	10.583%	$70.4082	$70.41	$70.40	$70.40
7 purchase totals =	$814.40		$915.3309	$915.34	$915.35	$915.20