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 $69.76   8.270%   $75.5292   $75.53   $75.55   $75.50  
  Purchase #2 $44.66   9.708%   $48.9956   $49.00   $49.00   $49.00  
  Purchase #3 $107.31   6.767%   $114.5717   $114.57   $114.55   $114.60  
  Purchase #4 $42.57   12.302%   $47.807   $47.81   $47.80   $47.80  
  Purchase #5 $59.32   11.257%   $65.9977   $66.00   $66.00   $66.00  
  Purchase #6 $236.41   5.517%   $249.4527   $249.45   $249.45   $249.50  
  Purchase #7 $248.96   8.284%   $269.5838   $269.58   $269.60   $269.60  
  7 purchase totals = $808.99       $871.9377   $871.94   $871.95   $872.00