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 $119.90   13.823%   $136.4738   $136.47   $136.45   $136.50  
  Purchase #2 $248.35   5.862%   $262.9083   $262.91   $262.90   $262.90  
  Purchase #3 $106.86   11.680%   $119.3412   $119.34   $119.35   $119.30  
  Purchase #4 $33.84   6.771%   $36.1313   $36.13   $36.15   $36.10  
  Purchase #5 $250.51   6.733%   $267.3768   $267.38   $267.40   $267.40  
  Purchase #6 $111.35   7.115%   $119.2726   $119.27   $119.25   $119.30  
  Purchase #7 $72.56   4.723%   $75.987   $75.99   $76.00   $76.00  
  7 purchase totals = $943.37       $1,017.4910   $1,017.49   $1,017.50   $1,017.50