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 $140.45   7.572%   $151.0849   $151.08   $151.10   $151.10  
  Purchase #2 $217.89   13.771%   $247.8956   $247.90   $247.90   $247.90  
  Purchase #3 $126.60   6.110%   $134.3353   $134.34   $134.35   $134.30  
  Purchase #4 $173.56   5.800%   $183.6265   $183.63   $183.65   $183.60  
  Purchase #5 $93.59   10.267%   $103.1989   $103.20   $103.20   $103.20  
  Purchase #6 $71.83   9.105%   $78.3701   $78.37   $78.35   $78.40  
  Purchase #7 $59.35   6.423%   $63.1621   $63.16   $63.15   $63.20  
  7 purchase totals = $883.27       $961.6734   $961.68   $961.70   $961.70