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 $190.37   13.127%   $215.3599   $215.36   $215.35   $215.40  
  Purchase #2 $47.41   7.642%   $51.0331   $51.03   $51.05   $51.00  
  Purchase #3 $69.36   4.238%   $72.2995   $72.30   $72.30   $72.30  
  Purchase #4 $98.45   6.620%   $104.9674   $104.97   $104.95   $105.00  
  Purchase #5 $237.80   8.779%   $258.6765   $258.68   $258.70   $258.70  
  Purchase #6 $15.75   8.423%   $17.0766   $17.08   $17.10   $17.10  
  Purchase #7 $211.40   7.773%   $227.8321   $227.83   $227.85   $227.80  
  7 purchase totals = $870.54       $947.2451   $947.25   $947.30   $947.30