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 $182.97   13.709%   $208.0534   $208.05   $208.05   $208.10  
  Purchase #2 $37.93   8.787%   $41.2629   $41.26   $41.25   $41.30  
  Purchase #3 $59.46   7.489%   $63.913   $63.91   $63.90   $63.90  
  Purchase #4 $172.40   12.523%   $193.9897   $193.99   $194.00   $194.00  
  Purchase #5 $70.38   5.714%   $74.4015   $74.40   $74.40   $74.40  
  Purchase #6 $103.76   11.750%   $115.9518   $115.95   $115.95   $116.00  
  Purchase #7 $111.55   13.344%   $126.4352   $126.44   $126.45   $126.40  
  7 purchase totals = $738.45       $824.0075   $824.00   $824.00   $824.10