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 $62.99   11.529%   $70.2521   $70.25   $70.25   $70.30  
  Purchase #2 $23.34   10.298%   $25.7436   $25.74   $25.75   $25.70  
  Purchase #3 $241.26   8.487%   $261.7357   $261.74   $261.75   $261.70  
  Purchase #4 $16.61   7.581%   $17.8692   $17.87   $17.85   $17.90  
  Purchase #5 $176.99   3.213%   $182.6767   $182.68   $182.70   $182.70  
  Purchase #6 $71.28   11.113%   $79.2013   $79.20   $79.20   $79.20  
  Purchase #7 $124.64   11.547%   $139.0322   $139.03   $139.05   $139.00  
  7 purchase totals = $717.11       $776.5108   $776.51   $776.55   $776.50