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 $122.76   8.131%   $132.7416   $132.74   $132.75   $132.70  
  Purchase #2 $146.53   8.237%   $158.5997   $158.60   $158.60   $158.60  
  Purchase #3 $51.42   4.679%   $53.8259   $53.83   $53.85   $53.80  
  Purchase #4 $31.89   13.854%   $36.308   $36.31   $36.30   $36.30  
  Purchase #5 $235.68   3.296%   $243.448   $243.45   $243.45   $243.40  
  Purchase #6 $227.88   13.411%   $258.441   $258.44   $258.45   $258.40  
  Purchase #7 $77.81   5.719%   $82.26   $82.26   $82.25   $82.30  
  7 purchase totals = $893.97       $965.6242   $965.63   $965.65   $965.50