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 $55.76   12.157%   $62.5387   $62.54   $62.55   $62.50  
  Purchase #2 $54.56   4.783%   $57.1696   $57.17   $57.15   $57.20  
  Purchase #3 $43.80   8.673%   $47.5988   $47.60   $47.60   $47.60  
  Purchase #4 $186.69   3.646%   $193.4967   $193.50   $193.50   $193.50  
  Purchase #5 $174.95   9.229%   $191.0961   $191.10   $191.10   $191.10  
  Purchase #6 $125.62   6.356%   $133.6044   $133.60   $133.60   $133.60  
  Purchase #7 $11.67   3.535%   $12.0825   $12.08   $12.10   $12.10  
  7 purchase totals = $653.05       $697.5868   $697.59   $697.60   $697.60