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 $104.37   13.729%   $118.699   $118.70   $118.70   $118.70  
  Purchase #2 $50.83   10.773%   $56.3059   $56.31   $56.30   $56.30  
  Purchase #3 $192.73   6.577%   $205.4059   $205.41   $205.40   $205.40  
  Purchase #4 $25.31   10.644%   $28.004   $28.00   $28.00   $28.00  
  Purchase #5 $85.96   7.533%   $92.4354   $92.44   $92.45   $92.40  
  Purchase #6 $153.61   6.375%   $163.4026   $163.40   $163.40   $163.40  
  Purchase #7 $100.63   13.436%   $114.1506   $114.15   $114.15   $114.20  
  7 purchase totals = $713.44       $778.4034   $778.41   $778.40   $778.40