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	$12.73	8.572%	$13.8212	$13.82	$13.80	$13.80
Purchase #2	$111.59	13.477%	$126.629	$126.63	$126.65	$126.60
Purchase #3	$75.75	10.742%	$83.8871	$83.89	$83.90	$83.90
Purchase #4	$43.76	4.619%	$45.7813	$45.78	$45.80	$45.80
Purchase #5	$44.74	4.126%	$46.586	$46.59	$46.60	$46.60
Purchase #6	$122.39	10.612%	$135.378	$135.38	$135.40	$135.40
Purchase #7	$87.43	9.250%	$95.5173	$95.52	$95.50	$95.50
7 purchase totals =	$498.39		$547.5999	$547.61	$547.65	$547.60