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 $244.32   12.520%   $274.9089   $274.91   $274.90   $274.90  
  Purchase #2 $197.81   4.663%   $207.0339   $207.03   $207.05   $207.00  
  Purchase #3 $29.38   13.295%   $33.2861   $33.29   $33.30   $33.30  
  Purchase #4 $217.88   12.158%   $244.3699   $244.37   $244.35   $244.40  
  Purchase #5 $139.45   8.642%   $151.5013   $151.50   $151.50   $151.50  
  Purchase #6 $208.37   4.436%   $217.6133   $217.61   $217.60   $217.60  
  Purchase #7 $158.25   12.228%   $177.6008   $177.60   $177.60   $177.60  
  7 purchase totals = $1,195.46       $1,306.3142   $1,306.31   $1,306.30   $1,306.30