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 $58.34   8.745%   $63.4418   $63.44   $63.45   $63.40  
  Purchase #2 $53.77   4.516%   $56.1983   $56.20   $56.20   $56.20  
  Purchase #3 $127.25   3.549%   $131.7661   $131.77   $131.75   $131.80  
  Purchase #4 $221.81   5.775%   $234.6195   $234.62   $234.60   $234.60  
  Purchase #5 $63.64   6.699%   $67.9032   $67.90   $67.90   $67.90  
  Purchase #6 $111.88   11.464%   $124.7059   $124.71   $124.70   $124.70  
  Purchase #7 $203.65   5.577%   $215.0076   $215.01   $215.00   $215.00  
  7 purchase totals = $840.34       $893.6424   $893.65   $893.60   $893.60