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 $177.86   13.702%   $202.2304   $202.23   $202.25   $202.20  
  Purchase #2 $75.76   11.239%   $84.2747   $84.27   $84.25   $84.30  
  Purchase #3 $81.64   5.759%   $86.3416   $86.34   $86.35   $86.30  
  Purchase #4 $196.29   11.198%   $218.2706   $218.27   $218.25   $218.30  
  Purchase #5 $156.62   7.434%   $168.2631   $168.26   $168.25   $168.30  
  Purchase #6 $41.91   8.515%   $45.4786   $45.48   $45.50   $45.50  
  Purchase #7 $136.66   8.577%   $148.3813   $148.38   $148.40   $148.40  
  7 purchase totals = $866.74       $953.2403   $953.23   $953.25   $953.30