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 $86.46   8.409%   $93.7304   $93.73   $93.75   $93.70  
  Purchase #2 $178.72   6.621%   $190.5531   $190.55   $190.55   $190.60  
  Purchase #3 $133.86   9.251%   $146.2434   $146.24   $146.25   $146.20  
  Purchase #4 $230.50   12.695%   $259.762   $259.76   $259.75   $259.80  
  Purchase #5 $56.41   6.662%   $60.168   $60.17   $60.15   $60.20  
  Purchase #6 $21.42   5.788%   $22.6598   $22.66   $22.65   $22.70  
  Purchase #7 $221.91   5.760%   $234.692   $234.69   $234.70   $234.70  
  7 purchase totals = $929.28       $1,007.8087   $1,007.80   $1,007.80   $1,007.90