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	$42.80	11.177%	$47.5838	$47.58	$47.60	$47.60
Purchase #2	$172.92	9.261%	$188.9341	$188.93	$188.95	$188.90
Purchase #3	$53.40	4.665%	$55.8911	$55.89	$55.90	$55.90
Purchase #4	$47.41	6.523%	$50.5026	$50.50	$50.50	$50.50
Purchase #5	$193.48	12.572%	$217.8043	$217.80	$217.80	$217.80
Purchase #6	$54.84	11.606%	$61.2047	$61.20	$61.20	$61.20
Purchase #7	$231.61	12.434%	$260.4084	$260.41	$260.40	$260.40
7 purchase totals =	$796.46		$882.3290	$882.31	$882.35	$882.30