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 $70.51   8.866%   $76.7614   $76.76   $76.75   $76.80  
  Purchase #2 $242.61   5.704%   $256.4485   $256.45   $256.45   $256.40  
  Purchase #3 $43.75   10.156%   $48.1933   $48.19   $48.20   $48.20  
  Purchase #4 $121.74   10.721%   $134.7917   $134.79   $134.80   $134.80  
  Purchase #5 $96.99   7.732%   $104.4893   $104.49   $104.50   $104.50  
  Purchase #6 $137.45   12.247%   $154.2835   $154.28   $154.30   $154.30  
  Purchase #7 $223.47   5.651%   $236.0983   $236.10   $236.10   $236.10  
  7 purchase totals = $936.52       $1,011.0660   $1,011.06   $1,011.10   $1,011.10