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 $207.83   13.815%   $236.5417   $236.54   $236.55   $236.50  
  Purchase #2 $53.90   7.615%   $58.0045   $58.00   $58.00   $58.00  
  Purchase #3 $237.48   8.787%   $258.3474   $258.35   $258.35   $258.30  
  Purchase #4 $198.87   9.358%   $217.4803   $217.48   $217.50   $217.50  
  Purchase #5 $58.94   13.457%   $66.8716   $66.87   $66.85   $66.90  
  Purchase #6 $12.93   5.806%   $13.6807   $13.68   $13.70   $13.70  
  Purchase #7 $18.66   10.209%   $20.565   $20.57   $20.55   $20.60  
  7 purchase totals = $788.61       $871.4912   $871.49   $871.50   $871.50