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 $105.41   8.687%   $114.567   $114.57   $114.55   $114.60  
  Purchase #2 $35.28   6.332%   $37.5139   $37.51   $37.50   $37.50  
  Purchase #3 $60.26   10.785%   $66.759   $66.76   $66.75   $66.80  
  Purchase #4 $29.52   13.755%   $33.5805   $33.58   $33.60   $33.60  
  Purchase #5 $239.28   9.218%   $261.3368   $261.34   $261.35   $261.30  
  Purchase #6 $122.81   9.592%   $134.5899   $134.59   $134.60   $134.60  
  Purchase #7 $146.88   3.241%   $151.6404   $151.64   $151.65   $151.60  
  7 purchase totals = $739.44       $799.9875   $799.99   $800.00   $800.00