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 $200.76   9.484%   $219.8001   $219.80   $219.80   $219.80  
  Purchase #2 $248.67   4.166%   $259.0296   $259.03   $259.05   $259.00  
  Purchase #3 $171.90   7.459%   $184.722   $184.72   $184.70   $184.70  
  Purchase #4 $59.86   12.518%   $67.3533   $67.35   $67.35   $67.40  
  Purchase #5 $195.79   6.341%   $208.205   $208.21   $208.20   $208.20  
  Purchase #6 $132.65   9.217%   $144.8764   $144.88   $144.90   $144.90  
  Purchase #7 $30.77   11.382%   $34.2722   $34.27   $34.25   $34.30  
  7 purchase totals = $1,040.40       $1,118.2586   $1,118.26   $1,118.25   $1,118.30