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 $42.62   10.372%   $47.0405   $47.04   $47.05   $47.00  
  Purchase #2 $187.46   7.261%   $201.0715   $201.07   $201.05   $201.10  
  Purchase #3 $77.58   4.391%   $80.9865   $80.99   $81.00   $81.00  
  Purchase #4 $75.58   8.861%   $82.2771   $82.28   $82.30   $82.30  
  Purchase #5 $83.57   10.585%   $92.4159   $92.42   $92.40   $92.40  
  Purchase #6 $33.85   4.818%   $35.4809   $35.48   $35.50   $35.50  
  Purchase #7 $224.50   13.844%   $255.5798   $255.58   $255.60   $255.60  
  7 purchase totals = $725.16       $794.8522   $794.86   $794.90   $794.90