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 $85.38   9.762%   $93.7148   $93.71   $93.70   $93.70  
  Purchase #2 $171.75   8.773%   $186.8176   $186.82   $186.80   $186.80  
  Purchase #3 $188.85   4.404%   $197.167   $197.17   $197.15   $197.20  
  Purchase #4 $248.46   10.337%   $274.1433   $274.14   $274.15   $274.10  
  Purchase #5 $165.76   5.643%   $175.1138   $175.11   $175.10   $175.10  
  Purchase #6 $209.27   10.177%   $230.5674   $230.57   $230.55   $230.60  
  Purchase #7 $174.27   9.172%   $190.254   $190.25   $190.25   $190.30  
  7 purchase totals = $1,243.74       $1,347.7779   $1,347.77   $1,347.70   $1,347.80