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	$80.82	11.661%	$90.2444	$90.24	$90.25	$90.20
Purchase #2	$19.45	9.777%	$21.3516	$21.35	$21.35	$21.40
Purchase #3	$20.38	12.284%	$22.8835	$22.88	$22.90	$22.90
Purchase #4	$10.51	8.271%	$11.3793	$11.38	$11.40	$11.40
Purchase #5	$122.92	13.294%	$139.261	$139.26	$139.25	$139.30
Purchase #6	$238.79	4.490%	$249.5117	$249.51	$249.50	$249.50
Purchase #7	$56.49	4.495%	$59.0292	$59.03	$59.05	$59.00
7 purchase totals =	$549.36		$593.6607	$593.65	$593.70	$593.70