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 $219.89   13.219%   $248.9573   $248.96   $248.95   $249.00  
  Purchase #2 $221.35   4.116%   $230.4608   $230.46   $230.45   $230.50  
  Purchase #3 $222.76   10.542%   $246.2434   $246.24   $246.25   $246.20  
  Purchase #4 $67.30   12.523%   $75.728   $75.73   $75.75   $75.70  
  Purchase #5 $210.95   5.442%   $222.4299   $222.43   $222.45   $222.40  
  Purchase #6 $151.27   8.796%   $164.5757   $164.58   $164.60   $164.60  
  Purchase #7 $147.65   12.747%   $166.4709   $166.47   $166.45   $166.50  
  7 purchase totals = $1,241.17       $1,354.8660   $1,354.87   $1,354.90   $1,354.90