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 $144.29   13.243%   $163.3983   $163.40   $163.40   $163.40  
  Purchase #2 $23.41   8.768%   $25.4626   $25.46   $25.45   $25.50  
  Purchase #3 $114.98   5.318%   $121.0946   $121.09   $121.10   $121.10  
  Purchase #4 $43.38   9.726%   $47.5991   $47.60   $47.60   $47.60  
  Purchase #5 $241.74   11.237%   $268.9043   $268.90   $268.90   $268.90  
  Purchase #6 $232.87   5.608%   $245.9293   $245.93   $245.95   $245.90  
  Purchase #7 $134.33   3.570%   $139.1256   $139.13   $139.15   $139.10  
  7 purchase totals = $935.00       $1,011.5138   $1,011.51   $1,011.55   $1,011.50