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 $115.25   10.534%   $127.3904   $127.39   $127.40   $127.40  
  Purchase #2 $176.83   3.808%   $183.5637   $183.56   $183.55   $183.60  
  Purchase #3 $118.82   3.805%   $123.3411   $123.34   $123.35   $123.30  
  Purchase #4 $40.52   11.303%   $45.1   $45.10   $45.10   $45.10  
  Purchase #5 $242.61   7.725%   $261.3516   $261.35   $261.35   $261.40  
  Purchase #6 $250.51   12.530%   $281.8989   $281.90   $281.90   $281.90  
  Purchase #7 $203.48   5.200%   $214.061   $214.06   $214.05   $214.10  
  7 purchase totals = $1,148.02       $1,236.7067   $1,236.70   $1,236.70   $1,236.80