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 $137.42   6.501%   $146.3537   $146.35   $146.35   $146.40  
  Purchase #2 $166.59   7.758%   $179.5141   $179.51   $179.50   $179.50  
  Purchase #3 $105.62   6.610%   $112.6015   $112.60   $112.60   $112.60  
  Purchase #4 $201.87   12.382%   $226.8655   $226.87   $226.85   $226.90  
  Purchase #5 $46.56   7.229%   $49.9258   $49.93   $49.95   $49.90  
  Purchase #6 $103.38   8.757%   $112.433   $112.43   $112.45   $112.40  
  Purchase #7 $114.57   6.781%   $122.339   $122.34   $122.35   $122.30  
  7 purchase totals = $876.01       $950.0326   $950.03   $950.05   $950.00