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 $59.33   10.660%   $65.6546   $65.65   $65.65   $65.70  
  Purchase #2 $222.95   12.509%   $250.8388   $250.84   $250.85   $250.80  
  Purchase #3 $10.66   8.652%   $11.5823   $11.58   $11.60   $11.60  
  Purchase #4 $217.26   11.501%   $242.2471   $242.25   $242.25   $242.20  
  Purchase #5 $36.61   10.452%   $40.4365   $40.44   $40.45   $40.40  
  Purchase #6 $173.91   5.248%   $183.0368   $183.04   $183.05   $183.00  
  Purchase #7 $92.36   10.469%   $102.0292   $102.03   $102.05   $102.00  
  7 purchase totals = $813.08       $895.8253   $895.83   $895.90   $895.70