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 $87.75   9.807%   $96.3556   $96.36   $96.35   $96.40  
  Purchase #2 $239.48   8.794%   $260.5399   $260.54   $260.55   $260.50  
  Purchase #3 $150.27   3.630%   $155.7248   $155.72   $155.70   $155.70  
  Purchase #4 $230.66   13.587%   $261.9998   $262.00   $262.00   $262.00  
  Purchase #5 $242.26   8.147%   $261.9969   $262.00   $262.00   $262.00  
  Purchase #6 $97.78   9.710%   $107.2744   $107.27   $107.25   $107.30  
  Purchase #7 $195.60   3.321%   $202.0959   $202.10   $202.10   $202.10  
  7 purchase totals = $1,243.80       $1,345.9873   $1,345.99   $1,345.95   $1,346.00