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 $92.35   12.751%   $104.1255   $104.13   $104.15   $104.10  
  Purchase #2 $216.66   10.524%   $239.4613   $239.46   $239.45   $239.50  
  Purchase #3 $11.60   12.321%   $13.0292   $13.03   $13.05   $13.00  
  Purchase #4 $162.31   8.692%   $176.418   $176.42   $176.40   $176.40  
  Purchase #5 $6.55   12.730%   $7.3838   $7.38   $7.40   $7.40  
  Purchase #6 $83.43   13.568%   $94.7498   $94.75   $94.75   $94.70  
  Purchase #7 $230.58   13.358%   $261.3809   $261.38   $261.40   $261.40  
  7 purchase totals = $803.48       $896.5485   $896.55   $896.60   $896.50