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	$23.68	3.257%	$24.4513	$24.45	$24.45	$24.50
Purchase #2	$189.49	11.106%	$210.5348	$210.53	$210.55	$210.50
Purchase #3	$74.32	12.359%	$83.5052	$83.51	$83.50	$83.50
Purchase #4	$96.83	9.125%	$105.6657	$105.67	$105.65	$105.70
Purchase #5	$36.40	13.839%	$41.4374	$41.44	$41.45	$41.40
Purchase #6	$205.63	11.127%	$228.5105	$228.51	$228.50	$228.50
Purchase #7	$88.31	7.452%	$94.8909	$94.89	$94.90	$94.90
7 purchase totals =	$714.66		$788.9958	$789.00	$789.00	$789.00