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 $223.38   11.444%   $248.9436   $248.94   $248.95   $248.90  
  Purchase #2 $76.64   6.492%   $81.6155   $81.62   $81.60   $81.60  
  Purchase #3 $11.71   4.598%   $12.2484   $12.25   $12.25   $12.20  
  Purchase #4 $190.88   9.213%   $208.4658   $208.47   $208.45   $208.50  
  Purchase #5 $43.95   3.242%   $45.3749   $45.37   $45.35   $45.40  
  Purchase #6 $86.95   11.241%   $96.724   $96.72   $96.70   $96.70  
  Purchase #7 $63.84   6.824%   $68.1964   $68.20   $68.20   $68.20  
  7 purchase totals = $697.35       $761.5686   $761.57   $761.50   $761.50