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 $230.26   13.554%   $261.4694   $261.47   $261.45   $261.50  
  Purchase #2 $174.35   9.223%   $190.4303   $190.43   $190.45   $190.40  
  Purchase #3 $218.83   8.526%   $237.4874   $237.49   $237.50   $237.50  
  Purchase #4 $111.26   13.402%   $126.1711   $126.17   $126.15   $126.20  
  Purchase #5 $202.27   13.779%   $230.1408   $230.14   $230.15   $230.10  
  Purchase #6 $43.47   3.284%   $44.8976   $44.90   $44.90   $44.90  
  Purchase #7 $143.55   3.508%   $148.5857   $148.59   $148.60   $148.60  
  7 purchase totals = $1,123.99       $1,239.1823   $1,239.19   $1,239.20   $1,239.20