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 $88.85   5.380%   $93.6301   $93.63   $93.65   $93.60  
  Purchase #2 $139.59   3.783%   $144.8707   $144.87   $144.85   $144.90  
  Purchase #3 $182.91   13.180%   $207.0175   $207.02   $207.00   $207.00  
  Purchase #4 $77.97   4.731%   $81.6588   $81.66   $81.65   $81.70  
  Purchase #5 $144.99   5.322%   $152.7064   $152.71   $152.70   $152.70  
  Purchase #6 $77.66   3.612%   $80.4651   $80.47   $80.45   $80.50  
  Purchase #7 $40.26   7.437%   $43.2541   $43.25   $43.25   $43.30  
  7 purchase totals = $752.23       $803.6027   $803.61   $803.55   $803.70