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	$241.80	12.773%	$272.6851	$272.69	$272.70	$272.70
Purchase #2	$49.42	10.473%	$54.5958	$54.60	$54.60	$54.60
Purchase #3	$133.44	8.630%	$144.9559	$144.96	$144.95	$145.00
Purchase #4	$242.90	11.681%	$271.2731	$271.27	$271.25	$271.30
Purchase #5	$79.74	4.470%	$83.3044	$83.30	$83.30	$83.30
Purchase #6	$136.51	5.177%	$143.5771	$143.58	$143.60	$143.60
Purchase #7	$216.57	13.346%	$245.4734	$245.47	$245.45	$245.50
7 purchase totals =	$1,100.38		$1,215.8648	$1,215.87	$1,215.85	$1,216.00