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 $247.98   7.783%   $267.2803   $267.28   $267.30   $267.30  
  Purchase #2 $250.82   4.380%   $261.8059   $261.81   $261.80   $261.80  
  Purchase #3 $134.36   12.513%   $151.1725   $151.17   $151.15   $151.20  
  Purchase #4 $60.75   7.246%   $65.1519   $65.15   $65.15   $65.20  
  Purchase #5 $81.83   3.686%   $84.8463   $84.85   $84.85   $84.80  
  Purchase #6 $44.56   13.656%   $50.6451   $50.65   $50.65   $50.60  
  Purchase #7 $66.88   3.412%   $69.1619   $69.16   $69.15   $69.20  
  7 purchase totals = $887.18       $950.0639   $950.07   $950.05   $950.10