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 $62.26   13.519%   $70.6769   $70.68   $70.70   $70.70  
  Purchase #2 $161.97   5.529%   $170.9253   $170.93   $170.95   $170.90  
  Purchase #3 $125.72   5.151%   $132.1958   $132.20   $132.20   $132.20  
  Purchase #4 $131.60   8.788%   $143.165   $143.17   $143.15   $143.20  
  Purchase #5 $90.25   10.464%   $99.6938   $99.69   $99.70   $99.70  
  Purchase #6 $42.81   12.810%   $48.294   $48.29   $48.30   $48.30  
  Purchase #7 $119.36   7.583%   $128.4111   $128.41   $128.40   $128.40  
  7 purchase totals = $733.97       $793.3619   $793.37   $793.40   $793.40