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 $239.61   13.837%   $272.7648   $272.76   $272.75   $272.80  
  Purchase #2 $119.76   9.617%   $131.2773   $131.28   $131.30   $131.30  
  Purchase #3 $188.32   9.684%   $206.5569   $206.56   $206.55   $206.60  
  Purchase #4 $45.62   11.630%   $50.9256   $50.93   $50.95   $50.90  
  Purchase #5 $167.37   9.821%   $183.8074   $183.81   $183.80   $183.80  
  Purchase #6 $197.55   5.301%   $208.0221   $208.02   $208.00   $208.00  
  Purchase #7 $25.31   11.490%   $28.2181   $28.22   $28.20   $28.20  
  7 purchase totals = $983.54       $1,081.5722   $1,081.58   $1,081.55   $1,081.60