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 $49.53   11.378%   $55.1655   $55.17   $55.15   $55.20  
  Purchase #2 $234.89   11.472%   $261.8366   $261.84   $261.85   $261.80  
  Purchase #3 $55.42   4.852%   $58.109   $58.11   $58.10   $58.10  
  Purchase #4 $164.74   7.352%   $176.8517   $176.85   $176.85   $176.90  
  Purchase #5 $82.91   11.612%   $92.5375   $92.54   $92.55   $92.50  
  Purchase #6 $84.98   5.173%   $89.376   $89.38   $89.40   $89.40  
  Purchase #7 $135.46   9.861%   $148.8177   $148.82   $148.80   $148.80  
  7 purchase totals = $807.93       $882.6940   $882.71   $882.70   $882.70