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	$53.89	6.687%	$57.4936	$57.49	$57.50	$57.50
Purchase #2	$221.48	3.686%	$229.6438	$229.64	$229.65	$229.60
Purchase #3	$205.86	4.410%	$214.9384	$214.94	$214.95	$214.90
Purchase #4	$77.87	9.739%	$85.4538	$85.45	$85.45	$85.50
Purchase #5	$54.68	3.492%	$56.5894	$56.59	$56.60	$56.60
Purchase #6	$129.56	11.552%	$144.5268	$144.53	$144.55	$144.50
Purchase #7	$117.86	12.449%	$132.5324	$132.53	$132.55	$132.50
7 purchase totals =	$861.20		$921.1782	$921.17	$921.25	$921.10