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 $248.27   5.507%   $261.9422   $261.94   $261.95   $261.90  
  Purchase #2 $55.85   3.864%   $58.008   $58.01   $58.00   $58.00  
  Purchase #3 $110.53   3.852%   $114.7876   $114.79   $114.80   $114.80  
  Purchase #4 $67.55   8.241%   $73.1168   $73.12   $73.10   $73.10  
  Purchase #5 $129.88   10.313%   $143.2745   $143.27   $143.25   $143.30  
  Purchase #6 $152.87   8.229%   $165.4497   $165.45   $165.45   $165.40  
  Purchase #7 $8.41   13.639%   $9.557   $9.56   $9.55   $9.60  
  7 purchase totals = $773.36       $826.1358   $826.14   $826.10   $826.10