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 $116.44   7.359%   $125.0088   $125.01   $125.00   $125.00  
  Purchase #2 $148.75   9.491%   $162.8679   $162.87   $162.85   $162.90  
  Purchase #3 $174.66   12.492%   $196.4785   $196.48   $196.50   $196.50  
  Purchase #4 $64.47   8.243%   $69.7843   $69.78   $69.80   $69.80  
  Purchase #5 $233.89   3.791%   $242.7568   $242.76   $242.75   $242.80  
  Purchase #6 $137.82   12.388%   $154.8931   $154.89   $154.90   $154.90  
  Purchase #7 $21.99   8.506%   $23.8605   $23.86   $23.85   $23.90  
  7 purchase totals = $898.02       $975.6499   $975.65   $975.65   $975.80