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 $130.48   8.769%   $141.9218   $141.92   $141.90   $141.90  
  Purchase #2 $98.99   6.316%   $105.2422   $105.24   $105.25   $105.20  
  Purchase #3 $223.41   4.433%   $233.3138   $233.31   $233.30   $233.30  
  Purchase #4 $57.38   4.674%   $60.0619   $60.06   $60.05   $60.10  
  Purchase #5 $59.46   10.609%   $65.7681   $65.77   $65.75   $65.80  
  Purchase #6 $240.74   8.466%   $261.121   $261.12   $261.10   $261.10  
  Purchase #7 $233.34   12.806%   $263.2215   $263.22   $263.20   $263.20  
  7 purchase totals = $1,043.80       $1,130.6503   $1,130.64   $1,130.55   $1,130.60