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 $88.54   12.553%   $99.6544   $99.65   $99.65   $99.70  
  Purchase #2 $179.72   8.332%   $194.6943   $194.69   $194.70   $194.70  
  Purchase #3 $84.60   6.548%   $90.1396   $90.14   $90.15   $90.10  
  Purchase #4 $199.44   4.309%   $208.0339   $208.03   $208.05   $208.00  
  Purchase #5 $126.93   10.432%   $140.1713   $140.17   $140.15   $140.20  
  Purchase #6 $199.35   4.166%   $207.6549   $207.65   $207.65   $207.70  
  Purchase #7 $24.46   6.239%   $25.9861   $25.99   $26.00   $26.00  
  7 purchase totals = $903.04       $966.3345   $966.32   $966.35   $966.40