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 $66.85   3.124%   $68.9384   $68.94   $68.95   $68.90  
  Purchase #2 $60.87   3.759%   $63.1581   $63.16   $63.15   $63.20  
  Purchase #3 $71.43   7.277%   $76.628   $76.63   $76.65   $76.60  
  Purchase #4 $30.29   7.776%   $32.6454   $32.65   $32.65   $32.60  
  Purchase #5 $250.78   5.742%   $265.1798   $265.18   $265.20   $265.20  
  Purchase #6 $152.64   4.526%   $159.5485   $159.55   $159.55   $159.50  
  Purchase #7 $122.80   9.525%   $134.4967   $134.50   $134.50   $134.50  
  7 purchase totals = $755.66       $800.5949   $800.61   $800.65   $800.50