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 $236.37   9.472%   $258.759   $258.76   $258.75   $258.80  
  Purchase #2 $114.38   9.341%   $125.0642   $125.06   $125.05   $125.10  
  Purchase #3 $73.73   3.423%   $76.2538   $76.25   $76.25   $76.30  
  Purchase #4 $31.92   10.837%   $35.3792   $35.38   $35.40   $35.40  
  Purchase #5 $88.39   5.244%   $93.0252   $93.03   $93.05   $93.00  
  Purchase #6 $135.70   9.592%   $148.7163   $148.72   $148.70   $148.70  
  Purchase #7 $240.57   3.769%   $249.6371   $249.64   $249.65   $249.60  
  7 purchase totals = $921.06       $986.8348   $986.84   $986.85   $986.90