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	$52.72	13.477%	$59.8251	$59.83	$59.85	$59.80
Purchase #2	$133.96	8.632%	$145.5234	$145.52	$145.50	$145.50
Purchase #3	$117.71	10.289%	$129.8212	$129.82	$129.80	$129.80
Purchase #4	$19.35	13.552%	$21.9723	$21.97	$21.95	$22.00
Purchase #5	$125.56	12.158%	$140.8256	$140.83	$140.85	$140.80
Purchase #6	$99.63	10.233%	$109.8251	$109.83	$109.85	$109.80
Purchase #7	$214.78	11.462%	$239.3981	$239.40	$239.40	$239.40
7 purchase totals =	$763.71		$847.1908	$847.20	$847.20	$847.10