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 $95.72   3.139%   $98.7247   $98.72   $98.70   $98.70  
  Purchase #2 $155.42   5.726%   $164.3193   $164.32   $164.30   $164.30  
  Purchase #3 $204.58   4.433%   $213.649   $213.65   $213.65   $213.60  
  Purchase #4 $237.95   8.462%   $258.0853   $258.09   $258.10   $258.10  
  Purchase #5 $169.36   10.853%   $187.7406   $187.74   $187.75   $187.70  
  Purchase #6 $69.67   4.653%   $72.9117   $72.91   $72.90   $72.90  
  Purchase #7 $118.99   13.721%   $135.3166   $135.32   $135.30   $135.30  
  7 purchase totals = $1,051.69       $1,130.7472   $1,130.75   $1,130.70   $1,130.60