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 $58.93   4.767%   $61.7392   $61.74   $61.75   $61.70  
  Purchase #2 $250.43   5.248%   $263.5726   $263.57   $263.55   $263.60  
  Purchase #3 $249.84   4.611%   $261.3601   $261.36   $261.35   $261.40  
  Purchase #4 $157.42   4.538%   $164.5637   $164.56   $164.55   $164.60  
  Purchase #5 $236.54   6.715%   $252.4237   $252.42   $252.40   $252.40  
  Purchase #6 $235.72   9.633%   $258.4269   $258.43   $258.45   $258.40  
  Purchase #7 $65.99   5.486%   $69.6102   $69.61   $69.60   $69.60  
  7 purchase totals = $1,254.87       $1,331.6964   $1,331.69   $1,331.65   $1,331.70