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 $71.34   8.280%   $77.247   $77.25   $77.25   $77.20  
  Purchase #2 $248.56   13.275%   $281.5563   $281.56   $281.55   $281.60  
  Purchase #3 $162.37   13.655%   $184.5416   $184.54   $184.55   $184.50  
  Purchase #4 $223.59   11.813%   $250.0027   $250.00   $250.00   $250.00  
  Purchase #5 $21.40   9.461%   $23.4247   $23.42   $23.40   $23.40  
  Purchase #6 $156.42   4.345%   $163.2164   $163.22   $163.20   $163.20  
  Purchase #7 $242.72   11.188%   $269.8755   $269.88   $269.90   $269.90  
  7 purchase totals = $1,126.40       $1,249.8642   $1,249.87   $1,249.85   $1,249.80