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 $236.85   13.708%   $269.3174   $269.32   $269.30   $269.30  
  Purchase #2 $211.71   13.293%   $239.8526   $239.85   $239.85   $239.90  
  Purchase #3 $121.60   4.295%   $126.8227   $126.82   $126.80   $126.80  
  Purchase #4 $24.72   7.527%   $26.5807   $26.58   $26.60   $26.60  
  Purchase #5 $112.73   3.385%   $116.5459   $116.55   $116.55   $116.50  
  Purchase #6 $216.76   12.509%   $243.8745   $243.87   $243.85   $243.90  
  Purchase #7 $71.63   7.406%   $76.9349   $76.93   $76.95   $76.90  
  7 purchase totals = $996.00       $1,099.9287   $1,099.92   $1,099.90   $1,099.90