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 $138.50   11.421%   $154.3181   $154.32   $154.30   $154.30  
  Purchase #2 $228.72   9.560%   $250.5856   $250.59   $250.60   $250.60  
  Purchase #3 $201.79   3.566%   $208.9858   $208.99   $209.00   $209.00  
  Purchase #4 $92.92   11.380%   $103.4943   $103.49   $103.50   $103.50  
  Purchase #5 $68.56   11.588%   $76.5047   $76.50   $76.50   $76.50  
  Purchase #6 $178.62   6.539%   $190.3   $190.30   $190.30   $190.30  
  Purchase #7 $152.57   8.136%   $164.9831   $164.98   $165.00   $165.00  
  7 purchase totals = $1,061.68       $1,149.1716   $1,149.17   $1,149.20   $1,149.20