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 $197.35   8.558%   $214.2392   $214.24   $214.25   $214.20  
  Purchase #2 $107.87   6.223%   $114.5828   $114.58   $114.60   $114.60  
  Purchase #3 $70.34   12.827%   $79.3625   $79.36   $79.35   $79.40  
  Purchase #4 $205.29   7.786%   $221.2739   $221.27   $221.25   $221.30  
  Purchase #5 $208.25   12.236%   $233.7315   $233.73   $233.75   $233.70  
  Purchase #6 $88.31   11.303%   $98.2917   $98.29   $98.30   $98.30  
  Purchase #7 $42.43   4.614%   $44.3877   $44.39   $44.40   $44.40  
  7 purchase totals = $919.84       $1,005.8693   $1,005.86   $1,005.90   $1,005.90