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 $240.67   13.495%   $273.1484   $273.15   $273.15   $273.10  
  Purchase #2 $48.43   13.411%   $54.9249   $54.92   $54.90   $54.90  
  Purchase #3 $45.61   13.183%   $51.6228   $51.62   $51.60   $51.60  
  Purchase #4 $125.69   12.641%   $141.5785   $141.58   $141.60   $141.60  
  Purchase #5 $104.36   8.546%   $113.2786   $113.28   $113.30   $113.30  
  Purchase #6 $174.93   13.180%   $197.9858   $197.99   $198.00   $198.00  
  Purchase #7 $189.77   5.812%   $200.7994   $200.80   $200.80   $200.80  
  7 purchase totals = $929.46       $1,033.3384   $1,033.34   $1,033.35   $1,033.30