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 $241.25   9.115%   $263.2399   $263.24   $263.25   $263.20  
  Purchase #2 $76.41   8.235%   $82.7024   $82.70   $82.70   $82.70  
  Purchase #3 $179.59   5.691%   $189.8105   $189.81   $189.80   $189.80  
  Purchase #4 $39.35   5.540%   $41.53   $41.53   $41.55   $41.50  
  Purchase #5 $104.88   6.267%   $111.4528   $111.45   $111.45   $111.50  
  Purchase #6 $14.90   8.550%   $16.174   $16.17   $16.15   $16.20  
  Purchase #7 $9.42   5.312%   $9.9204   $9.92   $9.90   $9.90  
  7 purchase totals = $665.80       $714.8300   $714.82   $714.80   $714.80