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 $73.76   3.182%   $76.107   $76.11   $76.10   $76.10  
  Purchase #2 $239.55   9.395%   $262.0557   $262.06   $262.05   $262.10  
  Purchase #3 $86.69   7.573%   $93.255   $93.26   $93.25   $93.30  
  Purchase #4 $119.68   12.723%   $134.9069   $134.91   $134.90   $134.90  
  Purchase #5 $24.74   5.111%   $26.0045   $26.00   $26.00   $26.00  
  Purchase #6 $223.88   4.536%   $234.0352   $234.04   $234.05   $234.00  
  Purchase #7 $149.82   4.602%   $156.7147   $156.71   $156.70   $156.70  
  7 purchase totals = $918.12       $983.0790   $983.09   $983.05   $983.10