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 $235.42   11.256%   $261.9189   $261.92   $261.90   $261.90  
  Purchase #2 $104.47   5.569%   $110.2879   $110.29   $110.30   $110.30  
  Purchase #3 $31.46   5.838%   $33.2966   $33.30   $33.30   $33.30  
  Purchase #4 $184.77   4.703%   $193.4597   $193.46   $193.45   $193.50  
  Purchase #5 $184.49   3.309%   $190.5948   $190.59   $190.60   $190.60  
  Purchase #6 $40.75   9.520%   $44.6294   $44.63   $44.65   $44.60  
  Purchase #7 $201.57   7.403%   $216.4922   $216.49   $216.50   $216.50  
  7 purchase totals = $982.93       $1,050.6795   $1,050.68   $1,050.70   $1,050.70