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 $154.66   6.469%   $164.665   $164.67   $164.65   $164.70  
  Purchase #2 $102.36   6.125%   $108.6296   $108.63   $108.65   $108.60  
  Purchase #3 $105.79   8.489%   $114.7705   $114.77   $114.75   $114.80  
  Purchase #4 $234.70   11.803%   $262.4016   $262.40   $262.40   $262.40  
  Purchase #5 $77.74   11.353%   $86.5658   $86.57   $86.55   $86.60  
  Purchase #6 $165.99   3.298%   $171.4644   $171.46   $171.45   $171.50  
  Purchase #7 $10.81   11.874%   $12.0936   $12.09   $12.10   $12.10  
  7 purchase totals = $852.05       $920.5905   $920.59   $920.55   $920.70