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 $111.41   13.307%   $126.2353   $126.24   $126.25   $126.20  
  Purchase #2 $104.83   8.700%   $113.9502   $113.95   $113.95   $114.00  
  Purchase #3 $245.70   11.283%   $273.4223   $273.42   $273.40   $273.40  
  Purchase #4 $233.91   4.763%   $245.0511   $245.05   $245.05   $245.10  
  Purchase #5 $109.62   7.373%   $117.7023   $117.70   $117.70   $117.70  
  Purchase #6 $65.61   8.575%   $71.2361   $71.24   $71.25   $71.20  
  Purchase #7 $232.45   11.273%   $258.6541   $258.65   $258.65   $258.70  
  7 purchase totals = $1,103.53       $1,206.2514   $1,206.25   $1,206.25   $1,206.30