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	$70.59	4.575%	$73.8195	$73.82	$73.80	$73.80
Purchase #2	$83.99	10.602%	$92.8946	$92.89	$92.90	$92.90
Purchase #3	$39.34	9.409%	$43.0415	$43.04	$43.05	$43.00
Purchase #4	$154.85	8.271%	$167.6576	$167.66	$167.65	$167.70
Purchase #5	$57.82	6.112%	$61.354	$61.35	$61.35	$61.40
Purchase #6	$175.77	10.630%	$194.4544	$194.45	$194.45	$194.50
Purchase #7	$9.40	11.730%	$10.5026	$10.50	$10.50	$10.50
7 purchase totals =	$591.76		$643.7242	$643.71	$643.70	$643.80