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 $55.53   5.300%   $58.4731   $58.47   $58.45   $58.50  
  Purchase #2 $82.71   4.653%   $86.5585   $86.56   $86.55   $86.60  
  Purchase #3 $173.60   10.592%   $191.9877   $191.99   $192.00   $192.00  
  Purchase #4 $49.55   3.447%   $51.258   $51.26   $51.25   $51.30  
  Purchase #5 $24.95   4.158%   $25.9874   $25.99   $26.00   $26.00  
  Purchase #6 $249.49   3.647%   $258.5889   $258.59   $258.60   $258.60  
  Purchase #7 $171.56   10.830%   $190.1399   $190.14   $190.15   $190.10  
  7 purchase totals = $807.39       $862.9935   $863.00   $863.00   $863.10