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 $207.76   7.110%   $222.5317   $222.53   $222.55   $222.50  
  Purchase #2 $163.57   8.154%   $176.9075   $176.91   $176.90   $176.90  
  Purchase #3 $53.38   4.562%   $55.8152   $55.82   $55.80   $55.80  
  Purchase #4 $224.37   12.146%   $251.622   $251.62   $251.60   $251.60  
  Purchase #5 $234.26   11.782%   $261.8605   $261.86   $261.85   $261.90  
  Purchase #6 $25.47   5.725%   $26.9282   $26.93   $26.95   $26.90  
  Purchase #7 $248.57   10.485%   $274.6326   $274.63   $274.65   $274.60  
  7 purchase totals = $1,157.38       $1,270.2977   $1,270.30   $1,270.30   $1,270.20