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 $235.83   10.773%   $261.236   $261.24   $261.25   $261.20  
  Purchase #2 $227.53   6.157%   $241.539   $241.54   $241.55   $241.50  
  Purchase #3 $28.98   9.503%   $31.734   $31.73   $31.75   $31.70  
  Purchase #4 $73.62   4.577%   $76.9896   $76.99   $77.00   $77.00  
  Purchase #5 $24.77   7.436%   $26.6119   $26.61   $26.60   $26.60  
  Purchase #6 $96.54   9.490%   $105.7016   $105.70   $105.70   $105.70  
  Purchase #7 $86.78   8.316%   $93.9966   $94.00   $94.00   $94.00  
  7 purchase totals = $774.05       $837.8087   $837.81   $837.85   $837.70