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 $117.71   8.158%   $127.3128   $127.31   $127.30   $127.30  
  Purchase #2 $208.91   3.696%   $216.6313   $216.63   $216.65   $216.60  
  Purchase #3 $52.64   9.133%   $57.4476   $57.45   $57.45   $57.40  
  Purchase #4 $167.41   4.146%   $174.3508   $174.35   $174.35   $174.40  
  Purchase #5 $111.42   12.510%   $125.3586   $125.36   $125.35   $125.40  
  Purchase #6 $250.37   4.282%   $261.0908   $261.09   $261.10   $261.10  
  Purchase #7 $21.75   12.584%   $24.487   $24.49   $24.50   $24.50  
  7 purchase totals = $930.21       $986.6789   $986.68   $986.70   $986.70