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 $227.97   4.856%   $239.0402   $239.04   $239.05   $239.00  
  Purchase #2 $239.26   13.143%   $270.7059   $270.71   $270.70   $270.70  
  Purchase #3 $96.49   7.198%   $103.4354   $103.44   $103.45   $103.40  
  Purchase #4 $108.76   5.385%   $114.6167   $114.62   $114.60   $114.60  
  Purchase #5 $47.79   12.664%   $53.8421   $53.84   $53.85   $53.80  
  Purchase #6 $45.88   6.163%   $48.7076   $48.71   $48.70   $48.70  
  Purchase #7 $232.35   5.780%   $245.7798   $245.78   $245.80   $245.80  
  7 purchase totals = $998.50       $1,076.1277   $1,076.14   $1,076.15   $1,076.00