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 $238.91   9.331%   $261.2027   $261.20   $261.20   $261.20  
  Purchase #2 $179.87   8.605%   $195.3478   $195.35   $195.35   $195.30  
  Purchase #3 $248.40   7.249%   $266.4065   $266.41   $266.40   $266.40  
  Purchase #4 $210.72   5.866%   $223.0808   $223.08   $223.10   $223.10  
  Purchase #5 $120.77   7.193%   $129.457   $129.46   $129.45   $129.50  
  Purchase #6 $89.66   8.780%   $97.5321   $97.53   $97.55   $97.50  
  Purchase #7 $25.25   10.457%   $27.8904   $27.89   $27.90   $27.90  
  7 purchase totals = $1,113.58       $1,200.9173   $1,200.92   $1,200.95   $1,200.90