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 $207.44   9.158%   $226.4374   $226.44   $226.45   $226.40  
  Purchase #2 $157.51   12.548%   $177.2744   $177.27   $177.25   $177.30  
  Purchase #3 $207.94   9.347%   $227.3762   $227.38   $227.40   $227.40  
  Purchase #4 $197.35   13.831%   $224.6455   $224.65   $224.65   $224.60  
  Purchase #5 $36.59   11.659%   $40.856   $40.86   $40.85   $40.90  
  Purchase #6 $208.37   3.526%   $215.7171   $215.72   $215.70   $215.70  
  Purchase #7 $226.76   13.350%   $257.0325   $257.03   $257.05   $257.00  
  7 purchase totals = $1,241.96       $1,369.3391   $1,369.35   $1,369.35   $1,369.30