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 $241.76   11.452%   $269.4464   $269.45   $269.45   $269.40  
  Purchase #2 $21.43   5.856%   $22.6849   $22.68   $22.70   $22.70  
  Purchase #3 $125.37   11.451%   $139.7261   $139.73   $139.75   $139.70  
  Purchase #4 $103.67   11.213%   $115.2945   $115.29   $115.30   $115.30  
  Purchase #5 $163.60   3.741%   $169.7203   $169.72   $169.70   $169.70  
  Purchase #6 $161.49   3.687%   $167.4441   $167.44   $167.45   $167.40  
  Purchase #7 $178.87   8.281%   $193.6822   $193.68   $193.70   $193.70  
  7 purchase totals = $996.19       $1,077.9985   $1,077.99   $1,078.05   $1,077.90