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 $126.63   13.231%   $143.3844   $143.38   $143.40   $143.40  
  Purchase #2 $111.45   7.721%   $120.0551   $120.06   $120.05   $120.10  
  Purchase #3 $165.37   8.663%   $179.696   $179.70   $179.70   $179.70  
  Purchase #4 $232.95   12.502%   $262.0734   $262.07   $262.05   $262.10  
  Purchase #5 $96.32   9.739%   $105.7006   $105.70   $105.70   $105.70  
  Purchase #6 $67.59   9.820%   $74.2273   $74.23   $74.25   $74.20  
  Purchase #7 $127.40   11.218%   $141.6917   $141.69   $141.70   $141.70  
  7 purchase totals = $927.71       $1,026.8285   $1,026.83   $1,026.85   $1,026.90