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 $198.28   3.504%   $205.2277   $205.23   $205.25   $205.20  
  Purchase #2 $241.76   13.321%   $273.9648   $273.96   $273.95   $274.00  
  Purchase #3 $114.99   8.124%   $124.3318   $124.33   $124.35   $124.30  
  Purchase #4 $161.28   11.179%   $179.3095   $179.31   $179.30   $179.30  
  Purchase #5 $52.99   3.777%   $54.9914   $54.99   $55.00   $55.00  
  Purchase #6 $50.81   7.773%   $54.7595   $54.76   $54.75   $54.80  
  Purchase #7 $25.25   4.644%   $26.4226   $26.42   $26.40   $26.40  
  7 purchase totals = $845.36       $919.0073   $919.00   $919.00   $919.00