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 $92.81   4.262%   $96.7656   $96.77   $96.75   $96.80  
  Purchase #2 $200.86   6.671%   $214.2594   $214.26   $214.25   $214.30  
  Purchase #3 $215.61   4.128%   $224.5104   $224.51   $224.50   $224.50  
  Purchase #4 $188.47   6.817%   $201.318   $201.32   $201.30   $201.30  
  Purchase #5 $168.95   11.710%   $188.734   $188.73   $188.75   $188.70  
  Purchase #6 $145.49   10.487%   $160.7475   $160.75   $160.75   $160.70  
  Purchase #7 $191.76   5.184%   $201.7008   $201.70   $201.70   $201.70  
  7 purchase totals = $1,203.95       $1,288.0357   $1,288.04   $1,288.00   $1,288.00