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 $164.57   8.766%   $178.9962   $179.00   $179.00   $179.00  
  Purchase #2 $114.72   4.261%   $119.6082   $119.61   $119.60   $119.60  
  Purchase #3 $24.35   10.417%   $26.8865   $26.89   $26.90   $26.90  
  Purchase #4 $85.80   5.484%   $90.5053   $90.51   $90.50   $90.50  
  Purchase #5 $86.85   7.813%   $93.6356   $93.64   $93.65   $93.60  
  Purchase #6 $59.99   13.506%   $68.0922   $68.09   $68.10   $68.10  
  Purchase #7 $117.41   11.225%   $130.5893   $130.59   $130.60   $130.60  
  7 purchase totals = $653.69       $708.3133   $708.33   $708.35   $708.30