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	$76.51	8.436%	$82.9644	$82.96	$82.95	$83.00
Purchase #2	$100.85	3.674%	$104.5552	$104.56	$104.55	$104.60
Purchase #3	$79.68	13.651%	$90.5571	$90.56	$90.55	$90.60
Purchase #4	$140.72	5.470%	$148.4174	$148.42	$148.40	$148.40
Purchase #5	$90.74	10.296%	$100.0826	$100.08	$100.10	$100.10
Purchase #6	$102.57	4.202%	$106.88	$106.88	$106.90	$106.90
Purchase #7	$212.61	6.475%	$226.3765	$226.38	$226.40	$226.40
7 purchase totals =	$803.68		$859.8332	$859.84	$859.85	$860.00