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 $23.85   8.715%   $25.9285   $25.93   $25.95   $25.90  
  Purchase #2 $140.86   12.211%   $158.0604   $158.06   $158.05   $158.10  
  Purchase #3 $123.80   5.138%   $130.1608   $130.16   $130.15   $130.20  
  Purchase #4 $114.54   8.835%   $124.6596   $124.66   $124.65   $124.70  
  Purchase #5 $198.44   4.568%   $207.5047   $207.50   $207.50   $207.50  
  Purchase #6 $68.96   5.819%   $72.9728   $72.97   $72.95   $73.00  
  Purchase #7 $249.28   5.722%   $263.5438   $263.54   $263.55   $263.50  
  7 purchase totals = $919.73       $982.8306   $982.82   $982.80   $982.90