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 $184.58   12.798%   $208.2025   $208.20   $208.20   $208.20  
  Purchase #2 $144.59   10.385%   $159.6057   $159.61   $159.60   $159.60  
  Purchase #3 $70.38   7.543%   $75.6888   $75.69   $75.70   $75.70  
  Purchase #4 $237.90   4.417%   $248.408   $248.41   $248.40   $248.40  
  Purchase #5 $54.87   4.331%   $57.2464   $57.25   $57.25   $57.20  
  Purchase #6 $141.60   5.328%   $149.1444   $149.14   $149.15   $149.10  
  Purchase #7 $56.39   9.530%   $61.764   $61.76   $61.75   $61.80  
  7 purchase totals = $890.31       $960.0598   $960.06   $960.05   $960.00