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 $57.62   11.459%   $64.2227   $64.22   $64.20   $64.20  
  Purchase #2 $231.38   11.744%   $258.5533   $258.55   $258.55   $258.60  
  Purchase #3 $114.25   10.520%   $126.2691   $126.27   $126.25   $126.30  
  Purchase #4 $190.51   3.856%   $197.8561   $197.86   $197.85   $197.90  
  Purchase #5 $41.93   11.680%   $46.8274   $46.83   $46.85   $46.80  
  Purchase #6 $200.35   12.387%   $225.1674   $225.17   $225.15   $225.20  
  Purchase #7 $133.98   10.743%   $148.3735   $148.37   $148.35   $148.40  
  7 purchase totals = $970.02       $1,067.2695   $1,067.27   $1,067.20   $1,067.40