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 $58.42   7.595%   $62.857   $62.86   $62.85   $62.90  
  Purchase #2 $16.67   7.773%   $17.9658   $17.97   $17.95   $18.00  
  Purchase #3 $237.45   5.685%   $250.949   $250.95   $250.95   $250.90  
  Purchase #4 $136.69   9.434%   $149.5853   $149.59   $149.60   $149.60  
  Purchase #5 $78.78   9.260%   $86.075   $86.08   $86.10   $86.10  
  Purchase #6 $182.95   13.806%   $208.2081   $208.21   $208.20   $208.20  
  Purchase #7 $145.83   4.371%   $152.2042   $152.20   $152.20   $152.20  
  7 purchase totals = $856.79       $927.8444   $927.86   $927.85   $927.90