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   13.276%   $65.6434   $65.64   $65.65   $65.60  
  Purchase #2 $122.28   8.865%   $133.1201   $133.12   $133.10   $133.10  
  Purchase #3 $87.87   6.509%   $93.5895   $93.59   $93.60   $93.60  
  Purchase #4 $55.66   7.348%   $59.7499   $59.75   $59.75   $59.70  
  Purchase #5 $8.65   12.554%   $9.7359   $9.74   $9.75   $9.70  
  Purchase #6 $131.61   11.705%   $147.015   $147.02   $147.00   $147.00  
  Purchase #7 $195.63   11.323%   $217.7812   $217.78   $217.80   $217.80  
  7 purchase totals = $659.65       $726.6350   $726.64   $726.65   $726.50