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 $62.96   8.617%   $68.3853   $68.39   $68.40   $68.40  
  Purchase #2 $208.40   11.499%   $232.3639   $232.36   $232.35   $232.40  
  Purchase #3 $216.42   10.783%   $239.7566   $239.76   $239.75   $239.80  
  Purchase #4 $8.94   8.693%   $9.7172   $9.72   $9.70   $9.70  
  Purchase #5 $33.66   4.154%   $35.0582   $35.06   $35.05   $35.10  
  Purchase #6 $208.74   6.685%   $222.6943   $222.69   $222.70   $222.70  
  Purchase #7 $53.70   3.230%   $55.4345   $55.43   $55.45   $55.40  
  7 purchase totals = $792.82       $863.4100   $863.41   $863.40   $863.50