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 $166.85   9.429%   $182.5823   $182.58   $182.60   $182.60  
  Purchase #2 $8.52   8.752%   $9.2657   $9.27   $9.25   $9.30  
  Purchase #3 $22.63   3.484%   $23.4184   $23.42   $23.40   $23.40  
  Purchase #4 $65.56   3.631%   $67.9405   $67.94   $67.95   $67.90  
  Purchase #5 $247.63   8.589%   $268.8989   $268.90   $268.90   $268.90  
  Purchase #6 $32.57   12.729%   $36.7158   $36.72   $36.70   $36.70  
  Purchase #7 $119.42   4.821%   $125.1772   $125.18   $125.20   $125.20  
  7 purchase totals = $663.18       $713.9988   $714.01   $714.00   $714.00