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 $20.76   5.131%   $21.8252   $21.83   $21.85   $21.80  
  Purchase #2 $12.99   3.617%   $13.4598   $13.46   $13.45   $13.50  
  Purchase #3 $197.91   9.510%   $216.7312   $216.73   $216.75   $216.70  
  Purchase #4 $135.29   6.722%   $144.3842   $144.38   $144.40   $144.40  
  Purchase #5 $191.86   11.797%   $214.4937   $214.49   $214.50   $214.50  
  Purchase #6 $50.63   9.552%   $55.4662   $55.47   $55.45   $55.50  
  Purchase #7 $166.47   12.184%   $186.7527   $186.75   $186.75   $186.80  
  7 purchase totals = $775.91       $853.1130   $853.11   $853.15   $853.20