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 $68.29   13.834%   $77.7372   $77.74   $77.75   $77.70  
  Purchase #2 $236.55   5.723%   $250.0878   $250.09   $250.10   $250.10  
  Purchase #3 $224.57   6.548%   $239.2748   $239.27   $239.25   $239.30  
  Purchase #4 $22.94   13.562%   $26.0511   $26.05   $26.05   $26.10  
  Purchase #5 $53.57   4.859%   $56.173   $56.17   $56.15   $56.20  
  Purchase #6 $49.99   4.358%   $52.1686   $52.17   $52.15   $52.20  
  Purchase #7 $196.43   5.495%   $207.2238   $207.22   $207.20   $207.20  
  7 purchase totals = $852.34       $908.7163   $908.71   $908.65   $908.80