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 $61.37   12.659%   $69.1388   $69.14   $69.15   $69.10  
  Purchase #2 $183.83   9.380%   $201.0733   $201.07   $201.05   $201.10  
  Purchase #3 $240.72   6.673%   $256.7832   $256.78   $256.80   $256.80  
  Purchase #4 $214.74   10.223%   $236.6929   $236.69   $236.70   $236.70  
  Purchase #5 $243.63   8.874%   $265.2497   $265.25   $265.25   $265.20  
  Purchase #6 $179.49   3.386%   $185.5675   $185.57   $185.55   $185.60  
  Purchase #7 $68.43   12.491%   $76.9776   $76.98   $77.00   $77.00  
  7 purchase totals = $1,192.21       $1,291.4830   $1,291.48   $1,291.50   $1,291.50