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 $246.99   7.694%   $265.9934   $265.99   $266.00   $266.00  
  Purchase #2 $165.75   12.547%   $186.5467   $186.55   $186.55   $186.50  
  Purchase #3 $9.95   13.566%   $11.2998   $11.30   $11.30   $11.30  
  Purchase #4 $26.38   7.735%   $28.4205   $28.42   $28.40   $28.40  
  Purchase #5 $42.30   6.725%   $45.1447   $45.14   $45.15   $45.10  
  Purchase #6 $56.80   10.436%   $62.7276   $62.73   $62.75   $62.70  
  Purchase #7 $79.35   6.855%   $84.7894   $84.79   $84.80   $84.80  
  7 purchase totals = $627.52       $684.9221   $684.92   $684.95   $684.80