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	$35.61	9.627%	$39.0382	$39.04	$39.05	$39.00
Purchase #2	$103.74	5.376%	$109.3171	$109.32	$109.30	$109.30
Purchase #3	$222.66	12.288%	$250.0205	$250.02	$250.00	$250.00
Purchase #4	$58.64	10.315%	$64.6887	$64.69	$64.70	$64.70
Purchase #5	$246.83	5.172%	$259.596	$259.60	$259.60	$259.60
Purchase #6	$84.83	11.387%	$94.4896	$94.49	$94.50	$94.50
Purchase #7	$132.60	5.151%	$139.4302	$139.43	$139.45	$139.40
7 purchase totals =	$884.91		$956.5803	$956.59	$956.60	$956.50