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 $105.91   12.161%   $118.7897   $118.79   $118.80   $118.80  
  Purchase #2 $196.45   5.797%   $207.8382   $207.84   $207.85   $207.80  
  Purchase #3 $170.58   13.687%   $193.9273   $193.93   $193.95   $193.90  
  Purchase #4 $61.88   6.481%   $65.8904   $65.89   $65.90   $65.90  
  Purchase #5 $224.81   11.371%   $250.3731   $250.37   $250.35   $250.40  
  Purchase #6 $240.58   9.345%   $263.0622   $263.06   $263.05   $263.10  
  Purchase #7 $180.63   3.286%   $186.5655   $186.57   $186.55   $186.60  
  7 purchase totals = $1,180.84       $1,286.4464   $1,286.45   $1,286.45   $1,286.50