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 $219.32   13.344%   $248.5861   $248.59   $248.60   $248.60  
  Purchase #2 $48.66   11.793%   $54.3985   $54.40   $54.40   $54.40  
  Purchase #3 $128.46   8.716%   $139.6566   $139.66   $139.65   $139.70  
  Purchase #4 $164.34   7.499%   $176.6639   $176.66   $176.65   $176.70  
  Purchase #5 $22.25   12.683%   $25.072   $25.07   $25.05   $25.10  
  Purchase #6 $241.41   13.602%   $274.2466   $274.25   $274.25   $274.20  
  Purchase #7 $109.87   4.736%   $115.0734   $115.07   $115.05   $115.10  
  7 purchase totals = $934.31       $1,033.6971   $1,033.70   $1,033.65   $1,033.80