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 $111.39   11.824%   $124.5608   $124.56   $124.55   $124.60  
  Purchase #2 $125.53   8.842%   $136.6294   $136.63   $136.65   $136.60  
  Purchase #3 $33.75   12.643%   $38.017   $38.02   $38.00   $38.00  
  Purchase #4 $43.67   11.328%   $48.6169   $48.62   $48.60   $48.60  
  Purchase #5 $242.32   7.810%   $261.2452   $261.25   $261.25   $261.20  
  Purchase #6 $146.49   3.191%   $151.1645   $151.16   $151.15   $151.20  
  Purchase #7 $203.61   9.401%   $222.7514   $222.75   $222.75   $222.80  
  7 purchase totals = $906.76       $982.9852   $982.99   $982.95   $983.00