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	$168.82	9.288%	$184.5	$184.50	$184.50	$184.50
Purchase #2	$215.25	3.527%	$222.8419	$222.84	$222.85	$222.80
Purchase #3	$12.80	4.604%	$13.3893	$13.39	$13.40	$13.40
Purchase #4	$188.54	7.838%	$203.3178	$203.32	$203.30	$203.30
Purchase #5	$131.59	5.857%	$139.2972	$139.30	$139.30	$139.30
Purchase #6	$63.39	5.210%	$66.6926	$66.69	$66.70	$66.70
Purchase #7	$29.25	4.588%	$30.592	$30.59	$30.60	$30.60
7 purchase totals =	$809.64		$860.6308	$860.63	$860.65	$860.60