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 $204.53   11.324%   $227.691   $227.69   $227.70   $227.70  
  Purchase #2 $71.97   5.804%   $76.1471   $76.15   $76.15   $76.10  
  Purchase #3 $175.83   3.176%   $181.4144   $181.41   $181.40   $181.40  
  Purchase #4 $67.48   13.502%   $76.5911   $76.59   $76.60   $76.60  
  Purchase #5 $203.46   11.521%   $226.9006   $226.90   $226.90   $226.90  
  Purchase #6 $197.75   7.162%   $211.9129   $211.91   $211.90   $211.90  
  Purchase #7 $75.70   3.135%   $78.0732   $78.07   $78.05   $78.10  
  7 purchase totals = $996.72       $1,078.7303   $1,078.72   $1,078.70   $1,078.70