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 $57.72   6.712%   $61.5942   $61.59   $61.60   $61.60  
  Purchase #2 $62.82   4.616%   $65.7198   $65.72   $65.70   $65.70  
  Purchase #3 $154.94   5.678%   $163.7375   $163.74   $163.75   $163.70  
  Purchase #4 $214.81   6.119%   $227.9542   $227.95   $227.95   $228.00  
  Purchase #5 $130.38   10.479%   $144.0425   $144.04   $144.05   $144.00  
  Purchase #6 $55.56   13.289%   $62.9434   $62.94   $62.95   $62.90  
  Purchase #7 $205.34   8.146%   $222.067   $222.07   $222.05   $222.10  
  7 purchase totals = $881.57       $948.0586   $948.05   $948.05   $948.00