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	$8.59	9.568%	$9.4119	$9.41	$9.40	$9.40
Purchase #2	$20.51	4.169%	$21.3651	$21.37	$21.35	$21.40
Purchase #3	$199.74	4.396%	$208.5206	$208.52	$208.50	$208.50
Purchase #4	$120.74	12.626%	$135.9846	$135.98	$136.00	$136.00
Purchase #5	$40.72	4.332%	$42.484	$42.48	$42.50	$42.50
Purchase #6	$49.55	13.675%	$56.326	$56.33	$56.35	$56.30
Purchase #7	$38.78	12.280%	$43.5422	$43.54	$43.55	$43.50
7 purchase totals =	$478.63		$517.6344	$517.63	$517.65	$517.60