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 $90.95   12.113%   $101.9668   $101.97   $101.95   $102.00  
  Purchase #2 $245.53   6.628%   $261.8037   $261.80   $261.80   $261.80  
  Purchase #3 $162.88   6.514%   $173.49   $173.49   $173.50   $173.50  
  Purchase #4 $73.45   9.872%   $80.701   $80.70   $80.70   $80.70  
  Purchase #5 $186.63   7.591%   $200.7971   $200.80   $200.80   $200.80  
  Purchase #6 $178.45   6.733%   $190.465   $190.47   $190.45   $190.50  
  Purchase #7 $30.51   3.331%   $31.5263   $31.53   $31.55   $31.50  
  7 purchase totals = $968.40       $1,040.7499   $1,040.76   $1,040.75   $1,040.80