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	$73.65	6.166%	$78.1913	$78.19	$78.20	$78.20
Purchase #2	$247.38	9.758%	$271.5193	$271.52	$271.50	$271.50
Purchase #3	$204.88	6.258%	$217.7014	$217.70	$217.70	$217.70
Purchase #4	$132.35	9.508%	$144.9338	$144.93	$144.95	$144.90
Purchase #5	$38.47	8.745%	$41.8342	$41.83	$41.85	$41.80
Purchase #6	$137.52	13.819%	$156.5239	$156.52	$156.50	$156.50
Purchase #7	$159.65	10.506%	$176.4228	$176.42	$176.40	$176.40
7 purchase totals =	$993.90		$1,087.1267	$1,087.11	$1,087.10	$1,087.00