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 $47.31   3.425%   $48.9304   $48.93   $48.95   $48.90  
  Purchase #2 $208.79   7.673%   $224.8105   $224.81   $224.80   $224.80  
  Purchase #3 $68.87   13.170%   $77.9402   $77.94   $77.95   $77.90  
  Purchase #4 $163.97   13.573%   $186.2256   $186.23   $186.25   $186.20  
  Purchase #5 $231.25   6.266%   $245.7401   $245.74   $245.75   $245.70  
  Purchase #6 $143.95   9.418%   $157.5072   $157.51   $157.50   $157.50  
  Purchase #7 $20.98   13.617%   $23.8368   $23.84   $23.85   $23.80  
  7 purchase totals = $885.12       $964.9908   $965.00   $965.05   $964.80