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 $235.35   11.567%   $262.5729   $262.57   $262.55   $262.60  
  Purchase #2 $185.81   12.301%   $208.6665   $208.67   $208.65   $208.70  
  Purchase #3 $134.94   13.147%   $152.6806   $152.68   $152.70   $152.70  
  Purchase #4 $102.67   3.172%   $105.9267   $105.93   $105.95   $105.90  
  Purchase #5 $221.95   13.737%   $252.4393   $252.44   $252.45   $252.40  
  Purchase #6 $30.84   9.137%   $33.6579   $33.66   $33.65   $33.70  
  Purchase #7 $249.68   3.187%   $257.6373   $257.64   $257.65   $257.60  
  7 purchase totals = $1,161.24       $1,273.5812   $1,273.59   $1,273.60   $1,273.60