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 $161.47   13.573%   $183.3863   $183.39   $183.40   $183.40  
  Purchase #2 $189.72   4.171%   $197.6332   $197.63   $197.65   $197.60  
  Purchase #3 $93.39   12.306%   $104.8826   $104.88   $104.90   $104.90  
  Purchase #4 $221.82   10.307%   $244.683   $244.68   $244.70   $244.70  
  Purchase #5 $82.33   9.813%   $90.409   $90.41   $90.40   $90.40  
  Purchase #6 $221.50   12.239%   $248.6094   $248.61   $248.60   $248.60  
  Purchase #7 $86.76   9.605%   $95.0933   $95.09   $95.10   $95.10  
  7 purchase totals = $1,056.99       $1,164.6968   $1,164.69   $1,164.75   $1,164.70