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 $52.69   11.848%   $58.9327   $58.93   $58.95   $58.90  
  Purchase #2 $225.69   13.343%   $255.8038   $255.80   $255.80   $255.80  
  Purchase #3 $242.32   11.260%   $269.6052   $269.61   $269.60   $269.60  
  Purchase #4 $187.63   7.241%   $201.2163   $201.22   $201.20   $201.20  
  Purchase #5 $73.25   4.411%   $76.4811   $76.48   $76.50   $76.50  
  Purchase #6 $195.72   5.140%   $205.78   $205.78   $205.80   $205.80  
  Purchase #7 $230.87   3.764%   $239.5599   $239.56   $239.55   $239.60  
  7 purchase totals = $1,208.17       $1,307.3790   $1,307.38   $1,307.40   $1,307.40