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	$249.50	6.808%	$266.486	$266.49	$266.50	$266.50
Purchase #2	$103.84	8.540%	$112.7079	$112.71	$112.70	$112.70
Purchase #3	$57.42	9.398%	$62.8163	$62.82	$62.80	$62.80
Purchase #4	$230.27	13.299%	$260.8936	$260.89	$260.90	$260.90
Purchase #5	$39.37	6.590%	$41.9645	$41.96	$41.95	$42.00
Purchase #6	$219.93	3.333%	$227.2603	$227.26	$227.25	$227.30
Purchase #7	$39.92	5.446%	$42.094	$42.09	$42.10	$42.10
7 purchase totals =	$940.25		$1,014.2226	$1,014.22	$1,014.20	$1,014.30