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 $64.83   11.469%   $72.2654   $72.27   $72.25   $72.30  
  Purchase #2 $195.69   4.731%   $204.9481   $204.95   $204.95   $204.90  
  Purchase #3 $65.83   11.728%   $73.5505   $73.55   $73.55   $73.60  
  Purchase #4 $54.96   4.398%   $57.3771   $57.38   $57.40   $57.40  
  Purchase #5 $5.63   8.255%   $6.0948   $6.09   $6.10   $6.10  
  Purchase #6 $247.50   9.213%   $270.3022   $270.30   $270.30   $270.30  
  Purchase #7 $248.95   11.565%   $277.7411   $277.74   $277.75   $277.70  
  7 purchase totals = $883.39       $962.2792   $962.28   $962.30   $962.30