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 $114.95   8.373%   $124.5748   $124.57   $124.55   $124.60  
  Purchase #2 $177.93   7.113%   $190.5862   $190.59   $190.60   $190.60  
  Purchase #3 $107.99   8.723%   $117.41   $117.41   $117.40   $117.40  
  Purchase #4 $151.49   11.713%   $169.234   $169.23   $169.25   $169.20  
  Purchase #5 $83.51   12.528%   $93.9721   $93.97   $93.95   $94.00  
  Purchase #6 $76.93   5.594%   $81.2335   $81.23   $81.25   $81.20  
  Purchase #7 $23.82   9.825%   $26.1603   $26.16   $26.15   $26.20  
  7 purchase totals = $736.62       $803.1709   $803.16   $803.15   $803.20