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 $195.89   13.350%   $222.0413   $222.04   $222.05   $222.00  
  Purchase #2 $214.53   10.356%   $236.7467   $236.75   $236.75   $236.70  
  Purchase #3 $162.80   6.724%   $173.7467   $173.75   $173.75   $173.70  
  Purchase #4 $248.41   4.565%   $259.7499   $259.75   $259.75   $259.70  
  Purchase #5 $114.62   6.867%   $122.491   $122.49   $122.50   $122.50  
  Purchase #6 $23.85   11.191%   $26.5191   $26.52   $26.50   $26.50  
  Purchase #7 $203.72   3.650%   $211.1558   $211.16   $211.15   $211.20  
  7 purchase totals = $1,163.82       $1,252.4505   $1,252.46   $1,252.45   $1,252.30