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 $59.61   4.543%   $62.3181   $62.32   $62.30   $62.30  
  Purchase #2 $122.41   6.420%   $130.2687   $130.27   $130.25   $130.30  
  Purchase #3 $193.30   12.278%   $217.0334   $217.03   $217.05   $217.00  
  Purchase #4 $43.83   13.415%   $49.7098   $49.71   $49.70   $49.70  
  Purchase #5 $195.73   5.407%   $206.3131   $206.31   $206.30   $206.30  
  Purchase #6 $121.33   13.425%   $137.6186   $137.62   $137.60   $137.60  
  Purchase #7 $127.73   9.226%   $139.5144   $139.51   $139.50   $139.50  
  7 purchase totals = $863.94       $942.7761   $942.77   $942.70   $942.70