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 $210.33   11.108%   $233.6935   $233.69   $233.70   $233.70  
  Purchase #2 $195.40   9.498%   $213.9591   $213.96   $213.95   $214.00  
  Purchase #3 $247.40   6.405%   $263.246   $263.25   $263.25   $263.20  
  Purchase #4 $69.25   13.579%   $78.6535   $78.65   $78.65   $78.70  
  Purchase #5 $72.88   4.284%   $76.0022   $76.00   $76.00   $76.00  
  Purchase #6 $116.34   7.483%   $125.0457   $125.05   $125.05   $125.00  
  Purchase #7 $250.68   3.335%   $259.0402   $259.04   $259.05   $259.00  
  7 purchase totals = $1,162.28       $1,249.6402   $1,249.64   $1,249.65   $1,249.60