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 $249.83   4.778%   $261.7669   $261.77   $261.75   $261.80  
  Purchase #2 $188.84   12.625%   $212.6811   $212.68   $212.70   $212.70  
  Purchase #3 $217.91   13.659%   $247.6743   $247.67   $247.65   $247.70  
  Purchase #4 $211.44   6.113%   $224.3653   $224.37   $224.35   $224.40  
  Purchase #5 $49.59   8.699%   $53.9038   $53.90   $53.90   $53.90  
  Purchase #6 $24.39   9.343%   $26.6688   $26.67   $26.65   $26.70  
  Purchase #7 $199.99   4.118%   $208.2256   $208.23   $208.25   $208.20  
  7 purchase totals = $1,141.99       $1,235.2858   $1,235.29   $1,235.25   $1,235.40