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 $165.89   4.548%   $173.4347   $173.43   $173.45   $173.40  
  Purchase #2 $35.54   11.178%   $39.5127   $39.51   $39.50   $39.50  
  Purchase #3 $93.65   13.658%   $106.4407   $106.44   $106.45   $106.40  
  Purchase #4 $111.99   8.439%   $121.4408   $121.44   $121.45   $121.40  
  Purchase #5 $70.54   11.152%   $78.4066   $78.41   $78.40   $78.40  
  Purchase #6 $104.87   8.763%   $114.0598   $114.06   $114.05   $114.10  
  Purchase #7 $81.33   6.789%   $86.8515   $86.85   $86.85   $86.90  
  7 purchase totals = $663.81       $720.1468   $720.14   $720.15   $720.10