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 $50.98   8.743%   $55.4372   $55.44   $55.45   $55.40  
  Purchase #2 $182.57   4.652%   $191.0632   $191.06   $191.05   $191.10  
  Purchase #3 $189.56   3.709%   $196.5908   $196.59   $196.60   $196.60  
  Purchase #4 $216.49   8.775%   $235.487   $235.49   $235.50   $235.50  
  Purchase #5 $142.79   4.358%   $149.0128   $149.01   $149.00   $149.00  
  Purchase #6 $74.89   7.778%   $80.7149   $80.71   $80.70   $80.70  
  Purchase #7 $50.59   10.685%   $55.9955   $56.00   $56.00   $56.00  
  7 purchase totals = $907.87       $964.3014   $964.30   $964.30   $964.30