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 $24.61   3.804%   $25.5462   $25.55   $25.55   $25.50  
  Purchase #2 $167.51   5.630%   $176.9408   $176.94   $176.95   $176.90  
  Purchase #3 $22.25   10.362%   $24.5555   $24.56   $24.55   $24.60  
  Purchase #4 $232.90   3.566%   $241.2052   $241.21   $241.20   $241.20  
  Purchase #5 $127.78   11.595%   $142.5961   $142.60   $142.60   $142.60  
  Purchase #6 $82.75   11.168%   $91.9915   $91.99   $92.00   $92.00  
  Purchase #7 $67.88   4.176%   $70.7147   $70.71   $70.70   $70.70  
  7 purchase totals = $725.68       $773.5500   $773.56   $773.55   $773.50