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 $239.42   9.227%   $261.5113   $261.51   $261.50   $261.50  
  Purchase #2 $53.88   8.763%   $58.6015   $58.60   $58.60   $58.60  
  Purchase #3 $127.47   3.451%   $131.869   $131.87   $131.85   $131.90  
  Purchase #4 $203.42   7.105%   $217.873   $217.87   $217.85   $217.90  
  Purchase #5 $87.63   11.788%   $97.9598   $97.96   $97.95   $98.00  
  Purchase #6 $128.60   9.515%   $140.8363   $140.84   $140.85   $140.80  
  Purchase #7 $121.34   13.480%   $137.6966   $137.70   $137.70   $137.70  
  7 purchase totals = $961.76       $1,046.3475   $1,046.35   $1,046.30   $1,046.40