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 $233.48   10.619%   $258.2732   $258.27   $258.25   $258.30  
  Purchase #2 $101.75   13.783%   $115.7742   $115.77   $115.75   $115.80  
  Purchase #3 $122.74   8.267%   $132.8869   $132.89   $132.90   $132.90  
  Purchase #4 $250.34   3.613%   $259.3848   $259.38   $259.40   $259.40  
  Purchase #5 $211.92   11.538%   $236.3713   $236.37   $236.35   $236.40  
  Purchase #6 $88.56   7.111%   $94.8575   $94.86   $94.85   $94.90  
  Purchase #7 $162.51   6.684%   $173.3722   $173.37   $173.35   $173.40  
  7 purchase totals = $1,171.30       $1,270.9201   $1,270.91   $1,270.85   $1,271.10