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 $55.66   6.456%   $59.2534   $59.25   $59.25   $59.30  
  Purchase #2 $179.83   3.285%   $185.7374   $185.74   $185.75   $185.70  
  Purchase #3 $230.65   5.228%   $242.7084   $242.71   $242.70   $242.70  
  Purchase #4 $240.87   8.692%   $261.8064   $261.81   $261.80   $261.80  
  Purchase #5 $48.55   5.365%   $51.1547   $51.15   $51.15   $51.20  
  Purchase #6 $34.68   13.529%   $39.3719   $39.37   $39.35   $39.40  
  Purchase #7 $9.82   13.221%   $11.1183   $11.12   $11.10   $11.10  
  7 purchase totals = $800.06       $851.1505   $851.15   $851.10   $851.20