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 $184.74   11.783%   $206.5079   $206.51   $206.50   $206.50  
  Purchase #2 $179.57   10.714%   $198.8091   $198.81   $198.80   $198.80  
  Purchase #3 $214.88   3.666%   $222.7575   $222.76   $222.75   $222.80  
  Purchase #4 $178.66   8.596%   $194.0176   $194.02   $194.00   $194.00  
  Purchase #5 $93.47   9.494%   $102.344   $102.34   $102.35   $102.30  
  Purchase #6 $108.68   5.455%   $114.6085   $114.61   $114.60   $114.60  
  Purchase #7 $183.29   10.244%   $202.0662   $202.07   $202.05   $202.10  
  7 purchase totals = $1,143.29       $1,241.1108   $1,241.12   $1,241.05   $1,241.10