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 $59.93   6.556%   $63.859   $63.86   $63.85   $63.90  
  Purchase #2 $237.94   11.828%   $266.0835   $266.08   $266.10   $266.10  
  Purchase #3 $208.44   6.565%   $222.1241   $222.12   $222.10   $222.10  
  Purchase #4 $88.56   4.292%   $92.361   $92.36   $92.35   $92.40  
  Purchase #5 $76.69   12.866%   $86.5569   $86.56   $86.55   $86.60  
  Purchase #6 $122.40   3.721%   $126.9545   $126.95   $126.95   $127.00  
  Purchase #7 $170.45   5.637%   $180.0583   $180.06   $180.05   $180.10  
  7 purchase totals = $964.41       $1,037.9973   $1,037.99   $1,037.95   $1,038.20