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 $123.58   11.194%   $137.4135   $137.41   $137.40   $137.40  
  Purchase #2 $59.57   10.624%   $65.8987   $65.90   $65.90   $65.90  
  Purchase #3 $205.80   8.328%   $222.939   $222.94   $222.95   $222.90  
  Purchase #4 $99.61   7.622%   $107.2023   $107.20   $107.20   $107.20  
  Purchase #5 $165.28   6.752%   $176.4397   $176.44   $176.45   $176.40  
  Purchase #6 $110.50   4.804%   $115.8084   $115.81   $115.80   $115.80  
  Purchase #7 $57.31   8.709%   $62.3011   $62.30   $62.30   $62.30  
  7 purchase totals = $821.65       $888.0027   $888.00   $888.00   $887.90