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 $23.73   12.755%   $26.7568   $26.76   $26.75   $26.80  
  Purchase #2 $113.73   5.234%   $119.6826   $119.68   $119.70   $119.70  
  Purchase #3 $44.41   9.112%   $48.4566   $48.46   $48.45   $48.50  
  Purchase #4 $106.39   7.579%   $114.4533   $114.45   $114.45   $114.50  
  Purchase #5 $245.58   4.521%   $256.6827   $256.68   $256.70   $256.70  
  Purchase #6 $41.85   8.649%   $45.4696   $45.47   $45.45   $45.50  
  Purchase #7 $243.48   6.783%   $259.9952   $260.00   $260.00   $260.00  
  7 purchase totals = $819.17       $871.4968   $871.50   $871.50   $871.70