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 $226.60   12.130%   $254.0866   $254.09   $254.10   $254.10  
  Purchase #2 $57.51   12.626%   $64.7712   $64.77   $64.75   $64.80  
  Purchase #3 $163.50   9.293%   $178.6941   $178.69   $178.70   $178.70  
  Purchase #4 $250.38   13.521%   $284.2339   $284.23   $284.25   $284.20  
  Purchase #5 $52.79   9.659%   $57.889   $57.89   $57.90   $57.90  
  Purchase #6 $108.64   5.662%   $114.7912   $114.79   $114.80   $114.80  
  Purchase #7 $45.43   3.346%   $46.9501   $46.95   $46.95   $47.00  
  7 purchase totals = $904.85       $1,001.4161   $1,001.41   $1,001.45   $1,001.50