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 $168.70   10.568%   $186.5282   $186.53   $186.55   $186.50  
  Purchase #2 $201.42   10.484%   $222.5369   $222.54   $222.55   $222.50  
  Purchase #3 $32.65   12.287%   $36.6617   $36.66   $36.65   $36.70  
  Purchase #4 $73.40   4.235%   $76.5085   $76.51   $76.50   $76.50  
  Purchase #5 $124.56   4.783%   $130.5177   $130.52   $130.50   $130.50  
  Purchase #6 $21.95   9.456%   $24.0256   $24.03   $24.05   $24.00  
  Purchase #7 $53.31   9.833%   $58.552   $58.55   $58.55   $58.60  
  7 purchase totals = $675.99       $735.3306   $735.34   $735.35   $735.30