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 $188.70   9.693%   $206.9907   $206.99   $207.00   $207.00  
  Purchase #2 $250.41   4.597%   $261.9213   $261.92   $261.90   $261.90  
  Purchase #3 $33.82   10.323%   $37.3112   $37.31   $37.30   $37.30  
  Purchase #4 $92.44   12.124%   $103.6474   $103.65   $103.65   $103.60  
  Purchase #5 $50.73   12.302%   $56.9708   $56.97   $56.95   $57.00  
  Purchase #6 $205.71   3.158%   $212.2063   $212.21   $212.20   $212.20  
  Purchase #7 $110.80   6.338%   $117.8225   $117.82   $117.80   $117.80  
  7 purchase totals = $932.61       $996.8702   $996.87   $996.80   $996.80