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	$38.87	8.709%	$42.2552	$42.26	$42.25	$42.30
Purchase #2	$87.54	11.706%	$97.7874	$97.79	$97.80	$97.80
Purchase #3	$25.88	6.687%	$27.6106	$27.61	$27.60	$27.60
Purchase #4	$140.56	8.327%	$152.2644	$152.26	$152.25	$152.30
Purchase #5	$167.88	11.716%	$187.5488	$187.55	$187.55	$187.50
Purchase #6	$154.64	3.638%	$160.2658	$160.27	$160.25	$160.30
Purchase #7	$112.41	6.615%	$119.8459	$119.85	$119.85	$119.80
7 purchase totals =	$727.78		$787.5781	$787.59	$787.55	$787.60