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 $208.38   8.584%   $226.2673   $226.27   $226.25   $226.30  
  Purchase #2 $84.73   10.383%   $93.5275   $93.53   $93.55   $93.50  
  Purchase #3 $115.84   12.658%   $130.503   $130.50   $130.50   $130.50  
  Purchase #4 $226.61   12.390%   $254.687   $254.69   $254.70   $254.70  
  Purchase #5 $153.43   8.434%   $166.3703   $166.37   $166.35   $166.40  
  Purchase #6 $21.54   8.811%   $23.4379   $23.44   $23.45   $23.40  
  Purchase #7 $135.59   13.693%   $154.1563   $154.16   $154.15   $154.20  
  7 purchase totals = $946.12       $1,048.9493   $1,048.96   $1,048.95   $1,049.00