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 $208.37   4.262%   $217.2507   $217.25   $217.25   $217.30  
  Purchase #2 $155.93   12.655%   $175.6629   $175.66   $175.65   $175.70  
  Purchase #3 $15.90   8.285%   $17.2173   $17.22   $17.20   $17.20  
  Purchase #4 $174.62   12.504%   $196.4545   $196.45   $196.45   $196.50  
  Purchase #5 $41.68   10.246%   $45.9505   $45.95   $45.95   $46.00  
  Purchase #6 $113.71   3.229%   $117.3817   $117.38   $117.40   $117.40  
  Purchase #7 $222.87   13.567%   $253.1068   $253.11   $253.10   $253.10  
  7 purchase totals = $933.08       $1,023.0244   $1,023.02   $1,023.00   $1,023.20