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	$46.32	13.733%	$52.6811	$52.68	$52.70	$52.70
Purchase #2	$152.97	3.597%	$158.4723	$158.47	$158.45	$158.50
Purchase #3	$137.82	10.725%	$152.6012	$152.60	$152.60	$152.60
Purchase #4	$52.75	3.161%	$54.4174	$54.42	$54.40	$54.40
Purchase #5	$41.36	4.814%	$43.3511	$43.35	$43.35	$43.40
Purchase #6	$155.66	12.134%	$174.5478	$174.55	$174.55	$174.50
Purchase #7	$147.95	10.685%	$163.7585	$163.76	$163.75	$163.80
7 purchase totals =	$734.83		$799.8294	$799.83	$799.80	$799.90