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 $198.62   5.110%   $208.7695   $208.77   $208.75   $208.80  
  Purchase #2 $248.99   13.376%   $282.2949   $282.29   $282.30   $282.30  
  Purchase #3 $75.30   12.448%   $84.6733   $84.67   $84.65   $84.70  
  Purchase #4 $62.77   6.347%   $66.754   $66.75   $66.75   $66.80  
  Purchase #5 $234.93   9.492%   $257.2296   $257.23   $257.25   $257.20  
  Purchase #6 $76.76   13.850%   $87.3913   $87.39   $87.40   $87.40  
  Purchase #7 $159.83   10.739%   $176.9941   $176.99   $177.00   $177.00  
  7 purchase totals = $1,057.20       $1,164.1067   $1,164.09   $1,164.10   $1,164.20