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 $57.95   7.281%   $62.1693   $62.17   $62.15   $62.20  
  Purchase #2 $52.81   6.739%   $56.3689   $56.37   $56.35   $56.40  
  Purchase #3 $164.46   10.777%   $182.1839   $182.18   $182.20   $182.20  
  Purchase #4 $71.68   9.785%   $78.6939   $78.69   $78.70   $78.70  
  Purchase #5 $123.49   6.742%   $131.8157   $131.82   $131.80   $131.80  
  Purchase #6 $115.34   8.775%   $125.4611   $125.46   $125.45   $125.50  
  Purchase #7 $82.31   3.258%   $84.9917   $84.99   $85.00   $85.00  
  7 purchase totals = $668.04       $721.6845   $721.68   $721.65   $721.80