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 $241.94   8.287%   $261.9896   $261.99   $262.00   $262.00  
  Purchase #2 $10.53   6.605%   $11.2255   $11.23   $11.25   $11.20  
  Purchase #3 $15.45   11.679%   $17.2544   $17.25   $17.25   $17.30  
  Purchase #4 $175.33   5.177%   $184.4068   $184.41   $184.40   $184.40  
  Purchase #5 $148.27   9.157%   $161.8471   $161.85   $161.85   $161.80  
  Purchase #6 $128.28   10.512%   $141.7648   $141.76   $141.75   $141.80  
  Purchase #7 $248.81   10.315%   $274.4748   $274.47   $274.45   $274.50  
  7 purchase totals = $968.61       $1,052.9630   $1,052.96   $1,052.95   $1,053.00