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 $61.49   10.574%   $67.992   $67.99   $68.00   $68.00  
  Purchase #2 $64.89   13.116%   $73.401   $73.40   $73.40   $73.40  
  Purchase #3 $243.46   13.844%   $277.1646   $277.16   $277.15   $277.20  
  Purchase #4 $16.25   8.855%   $17.6889   $17.69   $17.70   $17.70  
  Purchase #5 $24.56   6.586%   $26.1775   $26.18   $26.20   $26.20  
  Purchase #6 $32.59   3.436%   $33.7098   $33.71   $33.70   $33.70  
  Purchase #7 $186.75   7.504%   $200.7637   $200.76   $200.75   $200.80  
  7 purchase totals = $629.99       $696.8975   $696.89   $696.90   $697.00