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 $178.63   13.246%   $202.2913   $202.29   $202.30   $202.30  
  Purchase #2 $183.85   6.720%   $196.2047   $196.20   $196.20   $196.20  
  Purchase #3 $250.84   4.577%   $262.3209   $262.32   $262.30   $262.30  
  Purchase #4 $89.55   9.495%   $98.0528   $98.05   $98.05   $98.10  
  Purchase #5 $10.37   9.845%   $11.3909   $11.39   $11.40   $11.40  
  Purchase #6 $102.61   9.189%   $112.0388   $112.04   $112.05   $112.00  
  Purchase #7 $165.48   11.782%   $184.9769   $184.98   $185.00   $185.00  
  7 purchase totals = $981.33       $1,067.2763   $1,067.27   $1,067.30   $1,067.30