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 $207.63   8.719%   $225.7333   $225.73   $225.75   $225.70  
  Purchase #2 $7.43   3.733%   $7.7074   $7.71   $7.70   $7.70  
  Purchase #3 $234.74   8.309%   $254.2445   $254.24   $254.25   $254.20  
  Purchase #4 $182.71   13.334%   $207.0726   $207.07   $207.05   $207.10  
  Purchase #5 $233.55   6.569%   $248.8919   $248.89   $248.90   $248.90  
  Purchase #6 $242.66   5.191%   $255.2565   $255.26   $255.25   $255.30  
  Purchase #7 $176.72   10.696%   $195.622   $195.62   $195.60   $195.60  
  7 purchase totals = $1,285.44       $1,394.5282   $1,394.52   $1,394.50   $1,394.50