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	$70.60	11.356%	$78.6173	$78.62	$78.60	$78.60
Purchase #2	$43.64	6.745%	$46.5835	$46.58	$46.60	$46.60
Purchase #3	$113.35	12.466%	$127.4802	$127.48	$127.50	$127.50
Purchase #4	$175.84	6.500%	$187.2696	$187.27	$187.25	$187.30
Purchase #5	$107.36	4.753%	$112.4628	$112.46	$112.45	$112.50
Purchase #6	$205.62	3.421%	$212.6543	$212.65	$212.65	$212.70
Purchase #7	$12.93	6.349%	$13.7509	$13.75	$13.75	$13.80
7 purchase totals =	$729.34		$778.8186	$778.81	$778.80	$779.00