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 $64.64   11.391%   $72.0031   $72.00   $72.00   $72.00  
  Purchase #2 $110.48   3.189%   $114.0032   $114.00   $114.00   $114.00  
  Purchase #3 $90.28   6.566%   $96.2078   $96.21   $96.20   $96.20  
  Purchase #4 $116.99   13.259%   $132.5017   $132.50   $132.50   $132.50  
  Purchase #5 $103.99   9.324%   $113.686   $113.69   $113.70   $113.70  
  Purchase #6 $242.41   4.404%   $253.0857   $253.09   $253.10   $253.10  
  Purchase #7 $147.72   9.144%   $161.2275   $161.23   $161.25   $161.20  
  7 purchase totals = $876.51       $942.7150   $942.72   $942.75   $942.70