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 $193.54   5.360%   $203.9137   $203.91   $203.90   $203.90  
  Purchase #2 $178.49   6.779%   $190.5898   $190.59   $190.60   $190.60  
  Purchase #3 $124.44   6.807%   $132.9106   $132.91   $132.90   $132.90  
  Purchase #4 $190.98   5.554%   $201.587   $201.59   $201.60   $201.60  
  Purchase #5 $122.36   10.686%   $135.4354   $135.44   $135.45   $135.40  
  Purchase #6 $123.98   13.544%   $140.7719   $140.77   $140.75   $140.80  
  Purchase #7 $63.92   11.517%   $71.2817   $71.28   $71.30   $71.30  
  7 purchase totals = $997.71       $1,076.4901   $1,076.49   $1,076.50   $1,076.50