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	$180.67	5.439%	$190.4966	$190.50	$190.50	$190.50
Purchase #2	$176.59	3.430%	$182.647	$182.65	$182.65	$182.60
Purchase #3	$133.92	6.661%	$142.8404	$142.84	$142.85	$142.80
Purchase #4	$140.33	10.440%	$154.9805	$154.98	$155.00	$155.00
Purchase #5	$75.94	10.185%	$83.6745	$83.67	$83.65	$83.70
Purchase #6	$68.47	6.458%	$72.8918	$72.89	$72.90	$72.90
Purchase #7	$241.71	10.176%	$266.3064	$266.31	$266.30	$266.30
7 purchase totals =	$1,017.63		$1,093.8372	$1,093.84	$1,093.85	$1,093.80