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 $40.60   8.281%   $43.9621   $43.96   $43.95   $44.00  
  Purchase #2 $133.42   3.249%   $137.7548   $137.75   $137.75   $137.80  
  Purchase #3 $27.99   7.674%   $30.138   $30.14   $30.15   $30.10  
  Purchase #4 $174.86   10.260%   $192.8006   $192.80   $192.80   $192.80  
  Purchase #5 $117.83   6.340%   $125.3004   $125.30   $125.30   $125.30  
  Purchase #6 $142.98   13.716%   $162.5911   $162.59   $162.60   $162.60  
  Purchase #7 $92.26   9.520%   $101.0432   $101.04   $101.05   $101.00  
  7 purchase totals = $729.94       $793.5902   $793.58   $793.60   $793.60