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 $203.47   11.393%   $226.6513   $226.65   $226.65   $226.70  
  Purchase #2 $105.97   8.229%   $114.6903   $114.69   $114.70   $114.70  
  Purchase #3 $58.54   6.339%   $62.2509   $62.25   $62.25   $62.30  
  Purchase #4 $177.87   8.870%   $193.6471   $193.65   $193.65   $193.60  
  Purchase #5 $84.31   13.544%   $95.7289   $95.73   $95.75   $95.70  
  Purchase #6 $11.46   8.378%   $12.4201   $12.42   $12.40   $12.40  
  Purchase #7 $8.43   11.130%   $9.3683   $9.37   $9.35   $9.40  
  7 purchase totals = $650.05       $714.7569   $714.76   $714.75   $714.80