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	$24.42	11.845%	$27.3125	$27.31	$27.30	$27.30
Purchase #2	$23.70	3.376%	$24.5001	$24.50	$24.50	$24.50
Purchase #3	$87.43	3.839%	$90.7864	$90.79	$90.80	$90.80
Purchase #4	$82.38	3.865%	$85.564	$85.56	$85.55	$85.60
Purchase #5	$81.34	12.582%	$91.5742	$91.57	$91.55	$91.60
Purchase #6	$75.78	8.805%	$82.4524	$82.45	$82.45	$82.50
Purchase #7	$234.82	10.752%	$260.0678	$260.07	$260.05	$260.10
7 purchase totals =	$609.87		$662.2574	$662.25	$662.20	$662.40