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 $55.41   8.635%   $60.1947   $60.19   $60.20   $60.20  
  Purchase #2 $112.60   8.649%   $122.3388   $122.34   $122.35   $122.30  
  Purchase #3 $247.55   3.524%   $256.2737   $256.27   $256.25   $256.30  
  Purchase #4 $123.94   9.338%   $135.5135   $135.51   $135.50   $135.50  
  Purchase #5 $90.49   8.711%   $98.3726   $98.37   $98.35   $98.40  
  Purchase #6 $23.55   13.636%   $26.7613   $26.76   $26.75   $26.80  
  Purchase #7 $53.87   3.371%   $55.686   $55.69   $55.70   $55.70  
  7 purchase totals = $707.41       $755.1406   $755.13   $755.10   $755.20