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 $74.68   3.340%   $77.1743   $77.17   $77.15   $77.20  
  Purchase #2 $60.33   6.517%   $64.2617   $64.26   $64.25   $64.30  
  Purchase #3 $206.99   3.186%   $213.5847   $213.58   $213.60   $213.60  
  Purchase #4 $126.30   6.398%   $134.3807   $134.38   $134.40   $134.40  
  Purchase #5 $250.98   4.148%   $261.3907   $261.39   $261.40   $261.40  
  Purchase #6 $77.31   8.270%   $83.7035   $83.70   $83.70   $83.70  
  Purchase #7 $166.41   13.403%   $188.7139   $188.71   $188.70   $188.70  
  7 purchase totals = $963.00       $1,023.2095   $1,023.19   $1,023.20   $1,023.30