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	$20.40	9.666%	$22.3719	$22.37	$22.35	$22.40
Purchase #2	$74.85	8.114%	$80.9233	$80.92	$80.90	$80.90
Purchase #3	$153.78	9.135%	$167.8278	$167.83	$167.85	$167.80
Purchase #4	$45.35	13.300%	$51.3816	$51.38	$51.40	$51.40
Purchase #5	$132.85	4.189%	$138.4151	$138.42	$138.40	$138.40
Purchase #6	$188.87	6.175%	$200.5327	$200.53	$200.55	$200.50
Purchase #7	$170.25	11.870%	$190.4587	$190.46	$190.45	$190.50
7 purchase totals =	$786.35		$851.9111	$851.91	$851.90	$851.90