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 $188.87   11.744%   $211.0509   $211.05   $211.05   $211.10  
  Purchase #2 $114.86   3.859%   $119.2924   $119.29   $119.30   $119.30  
  Purchase #3 $47.95   7.318%   $51.459   $51.46   $51.45   $51.50  
  Purchase #4 $225.97   3.537%   $233.9626   $233.96   $233.95   $234.00  
  Purchase #5 $157.61   9.516%   $172.6082   $172.61   $172.60   $172.60  
  Purchase #6 $236.55   9.359%   $258.6887   $258.69   $258.70   $258.70  
  Purchase #7 $172.62   3.175%   $178.1007   $178.10   $178.10   $178.10  
  7 purchase totals = $1,144.43       $1,225.1625   $1,225.16   $1,225.15   $1,225.30