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 $180.82   8.161%   $195.5767   $195.58   $195.60   $195.60  
  Purchase #2 $28.75   13.847%   $32.731   $32.73   $32.75   $32.70  
  Purchase #3 $220.81   9.459%   $241.6964   $241.70   $241.70   $241.70  
  Purchase #4 $173.88   3.309%   $179.6337   $179.63   $179.65   $179.60  
  Purchase #5 $50.76   13.708%   $57.7182   $57.72   $57.70   $57.70  
  Purchase #6 $11.35   4.414%   $11.851   $11.85   $11.85   $11.90  
  Purchase #7 $161.71   12.811%   $182.4267   $182.43   $182.45   $182.40  
  7 purchase totals = $828.08       $901.6337   $901.64   $901.70   $901.60