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 $41.85   3.536%   $43.3298   $43.33   $43.35   $43.30  
  Purchase #2 $176.85   7.578%   $190.2517   $190.25   $190.25   $190.30  
  Purchase #3 $196.49   8.545%   $213.2801   $213.28   $213.30   $213.30  
  Purchase #4 $236.32   7.486%   $254.0109   $254.01   $254.00   $254.00  
  Purchase #5 $101.88   7.473%   $109.4935   $109.49   $109.50   $109.50  
  Purchase #6 $28.99   6.235%   $30.7975   $30.80   $30.80   $30.80  
  Purchase #7 $49.83   9.652%   $54.6396   $54.64   $54.65   $54.60  
  7 purchase totals = $832.21       $895.8031   $895.80   $895.85   $895.80