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	$11.46	10.808%	$12.6986	$12.70	$12.70	$12.70
Purchase #2	$35.54	3.661%	$36.8411	$36.84	$36.85	$36.80
Purchase #3	$100.75	10.573%	$111.4023	$111.40	$111.40	$111.40
Purchase #4	$174.90	11.215%	$194.515	$194.52	$194.50	$194.50
Purchase #5	$73.40	11.723%	$82.0047	$82.00	$82.00	$82.00
Purchase #6	$126.31	11.357%	$140.655	$140.66	$140.65	$140.70
Purchase #7	$154.45	4.462%	$161.3416	$161.34	$161.35	$161.30
7 purchase totals =	$676.81		$739.4583	$739.46	$739.45	$739.40