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 $196.47   6.254%   $208.7572   $208.76   $208.75   $208.80  
  Purchase #2 $182.35   12.711%   $205.5285   $205.53   $205.55   $205.50  
  Purchase #3 $169.76   7.214%   $182.0065   $182.01   $182.00   $182.00  
  Purchase #4 $138.34   11.839%   $154.7181   $154.72   $154.70   $154.70  
  Purchase #5 $124.57   9.694%   $136.6458   $136.65   $136.65   $136.60  
  Purchase #6 $58.32   10.412%   $64.3923   $64.39   $64.40   $64.40  
  Purchase #7 $14.50   13.474%   $16.4537   $16.45   $16.45   $16.50  
  7 purchase totals = $884.31       $968.5021   $968.51   $968.50   $968.50