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 $17.95   8.790%   $19.5278   $19.53   $19.55   $19.50  
  Purchase #2 $134.55   8.737%   $146.3056   $146.31   $146.30   $146.30  
  Purchase #3 $82.32   4.758%   $86.2368   $86.24   $86.25   $86.20  
  Purchase #4 $67.51   3.139%   $69.6291   $69.63   $69.65   $69.60  
  Purchase #5 $176.96   9.349%   $193.504   $193.50   $193.50   $193.50  
  Purchase #6 $201.96   11.295%   $224.7714   $224.77   $224.75   $224.80  
  Purchase #7 $30.46   11.492%   $33.9605   $33.96   $33.95   $34.00  
  7 purchase totals = $711.71       $773.9352   $773.94   $773.95   $773.90