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 $176.80   9.134%   $192.9489   $192.95   $192.95   $192.90  
  Purchase #2 $15.39   12.155%   $17.2607   $17.26   $17.25   $17.30  
  Purchase #3 $212.95   12.613%   $239.8094   $239.81   $239.80   $239.80  
  Purchase #4 $69.93   6.323%   $74.3517   $74.35   $74.35   $74.40  
  Purchase #5 $72.89   6.827%   $77.8662   $77.87   $77.85   $77.90  
  Purchase #6 $224.91   5.179%   $236.5581   $236.56   $236.55   $236.60  
  Purchase #7 $25.72   12.248%   $28.8702   $28.87   $28.85   $28.90  
  7 purchase totals = $798.59       $867.6652   $867.67   $867.60   $867.80