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 $175.30   5.292%   $184.5769   $184.58   $184.60   $184.60  
  Purchase #2 $154.99   6.286%   $164.7327   $164.73   $164.75   $164.70  
  Purchase #3 $222.91   11.289%   $248.0743   $248.07   $248.05   $248.10  
  Purchase #4 $218.61   8.103%   $236.324   $236.32   $236.30   $236.30  
  Purchase #5 $115.62   7.148%   $123.8845   $123.88   $123.90   $123.90  
  Purchase #6 $27.49   8.758%   $29.8976   $29.90   $29.90   $29.90  
  Purchase #7 $246.73   10.565%   $272.797   $272.80   $272.80   $272.80  
  7 purchase totals = $1,161.65       $1,260.2870   $1,260.28   $1,260.30   $1,260.30