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 $67.81   13.209%   $76.767   $76.77   $76.75   $76.80  
  Purchase #2 $235.45   9.857%   $258.6583   $258.66   $258.65   $258.70  
  Purchase #3 $56.71   4.526%   $59.2767   $59.28   $59.30   $59.30  
  Purchase #4 $33.61   6.523%   $35.8024   $35.80   $35.80   $35.80  
  Purchase #5 $75.99   11.466%   $84.703   $84.70   $84.70   $84.70  
  Purchase #6 $35.48   5.868%   $37.562   $37.56   $37.55   $37.60  
  Purchase #7 $130.76   11.379%   $145.6392   $145.64   $145.65   $145.60  
  7 purchase totals = $635.81       $698.4086   $698.41   $698.40   $698.50