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 $228.93   8.758%   $248.9797   $248.98   $249.00   $249.00  
  Purchase #2 $66.73   8.439%   $72.3613   $72.36   $72.35   $72.40  
  Purchase #3 $123.70   4.423%   $129.1713   $129.17   $129.15   $129.20  
  Purchase #4 $243.46   9.495%   $266.5765   $266.58   $266.60   $266.60  
  Purchase #5 $193.43   12.242%   $217.1097   $217.11   $217.10   $217.10  
  Purchase #6 $50.57   5.359%   $53.28   $53.28   $53.30   $53.30  
  Purchase #7 $180.38   9.143%   $196.8721   $196.87   $196.85   $196.90  
  7 purchase totals = $1,087.20       $1,184.3506   $1,184.35   $1,184.35   $1,184.50