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 $34.37   5.565%   $36.2827   $36.28   $36.30   $36.30  
  Purchase #2 $199.51   8.138%   $215.7461   $215.75   $215.75   $215.70  
  Purchase #3 $226.66   10.664%   $250.831   $250.83   $250.85   $250.80  
  Purchase #4 $125.87   7.189%   $134.9188   $134.92   $134.90   $134.90  
  Purchase #5 $143.76   7.347%   $154.322   $154.32   $154.30   $154.30  
  Purchase #6 $125.73   12.576%   $141.5418   $141.54   $141.55   $141.50  
  Purchase #7 $239.83   9.257%   $262.0311   $262.03   $262.05   $262.00  
  7 purchase totals = $1,095.73       $1,195.6735   $1,195.67   $1,195.70   $1,195.50