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	$51.89	8.449%	$56.2742	$56.27	$56.25	$56.30
Purchase #2	$10.31	6.566%	$10.987	$10.99	$11.00	$11.00
Purchase #3	$126.93	5.424%	$133.8147	$133.81	$133.80	$133.80
Purchase #4	$155.53	12.755%	$175.3679	$175.37	$175.35	$175.40
Purchase #5	$49.56	8.240%	$53.6437	$53.64	$53.65	$53.60
Purchase #6	$103.55	8.673%	$112.5309	$112.53	$112.55	$112.50
Purchase #7	$90.48	9.389%	$98.9752	$98.98	$99.00	$99.00
7 purchase totals =	$588.25		$641.5936	$641.59	$641.60	$641.60