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 $86.82   7.410%   $93.2534   $93.25   $93.25   $93.30  
  Purchase #2 $185.31   8.853%   $201.7155   $201.72   $201.70   $201.70  
  Purchase #3 $208.82   3.330%   $215.7737   $215.77   $215.75   $215.80  
  Purchase #4 $26.88   11.477%   $29.965   $29.97   $29.95   $30.00  
  Purchase #5 $193.76   11.273%   $215.6026   $215.60   $215.60   $215.60  
  Purchase #6 $65.50   10.324%   $72.2622   $72.26   $72.25   $72.30  
  Purchase #7 $123.77   12.155%   $138.8142   $138.81   $138.80   $138.80  
  7 purchase totals = $890.86       $967.3866   $967.38   $967.30   $967.50