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 $56.47   4.266%   $58.879   $58.88   $58.90   $58.90  
  Purchase #2 $76.46   13.225%   $86.5718   $86.57   $86.55   $86.60  
  Purchase #3 $22.48   13.175%   $25.4417   $25.44   $25.45   $25.40  
  Purchase #4 $226.26   3.275%   $233.67   $233.67   $233.65   $233.70  
  Purchase #5 $241.87   10.671%   $267.6799   $267.68   $267.70   $267.70  
  Purchase #6 $70.75   13.681%   $80.4293   $80.43   $80.45   $80.40  
  Purchase #7 $201.66   11.587%   $225.0263   $225.03   $225.05   $225.00  
  7 purchase totals = $895.95       $977.6980   $977.70   $977.75   $977.70