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	$46.53	8.358%	$50.419	$50.42	$50.40	$50.40
Purchase #2	$76.72	11.192%	$85.3065	$85.31	$85.30	$85.30
Purchase #3	$112.54	13.622%	$127.8702	$127.87	$127.85	$127.90
Purchase #4	$177.61	13.125%	$200.9213	$200.92	$200.90	$200.90
Purchase #5	$174.51	9.244%	$190.6417	$190.64	$190.65	$190.60
Purchase #6	$169.28	9.630%	$185.5817	$185.58	$185.60	$185.60
Purchase #7	$126.39	6.800%	$134.9845	$134.98	$135.00	$135.00
7 purchase totals =	$883.58		$975.7249	$975.72	$975.70	$975.70