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 $136.54   8.494%   $148.1377   $148.14   $148.15   $148.10  
  Purchase #2 $176.55   3.566%   $182.8458   $182.85   $182.85   $182.80  
  Purchase #3 $161.47   7.796%   $174.0582   $174.06   $174.05   $174.10  
  Purchase #4 $162.58   6.772%   $173.5899   $173.59   $173.60   $173.60  
  Purchase #5 $198.76   4.866%   $208.4317   $208.43   $208.45   $208.40  
  Purchase #6 $249.63   12.231%   $280.1622   $280.16   $280.15   $280.20  
  Purchase #7 $217.68   10.846%   $241.2896   $241.29   $241.30   $241.30  
  7 purchase totals = $1,303.21       $1,408.5151   $1,408.52   $1,408.55   $1,408.50