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 $61.57   9.690%   $67.5361   $67.54   $67.55   $67.50  
  Purchase #2 $55.79   6.383%   $59.3511   $59.35   $59.35   $59.40  
  Purchase #3 $180.25   8.365%   $195.3279   $195.33   $195.35   $195.30  
  Purchase #4 $233.70   13.389%   $264.9901   $264.99   $265.00   $265.00  
  Purchase #5 $130.61   3.383%   $135.0285   $135.03   $135.05   $135.00  
  Purchase #6 $103.79   9.671%   $113.8275   $113.83   $113.85   $113.80  
  Purchase #7 $217.68   5.287%   $229.1887   $229.19   $229.20   $229.20  
  7 purchase totals = $983.39       $1,065.2499   $1,065.26   $1,065.35   $1,065.20