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 $126.36   10.164%   $139.2032   $139.20   $139.20   $139.20  
  Purchase #2 $73.39   3.544%   $75.9909   $75.99   $76.00   $76.00  
  Purchase #3 $31.61   6.759%   $33.7465   $33.75   $33.75   $33.70  
  Purchase #4 $121.87   13.182%   $137.9349   $137.93   $137.95   $137.90  
  Purchase #5 $64.35   11.192%   $71.5521   $71.55   $71.55   $71.60  
  Purchase #6 $226.76   3.225%   $234.073   $234.07   $234.05   $234.10  
  Purchase #7 $52.87   7.247%   $56.7015   $56.70   $56.70   $56.70  
  7 purchase totals = $697.21       $749.2021   $749.19   $749.20   $749.20