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 $39.32   9.739%   $43.1494   $43.15   $43.15   $43.10  
  Purchase #2 $185.43   4.703%   $194.1508   $194.15   $194.15   $194.20  
  Purchase #3 $90.79   8.691%   $98.6806   $98.68   $98.70   $98.70  
  Purchase #4 $61.61   8.207%   $66.6663   $66.67   $66.65   $66.70  
  Purchase #5 $14.97   3.802%   $15.5392   $15.54   $15.55   $15.50  
  Purchase #6 $230.87   8.431%   $250.3346   $250.33   $250.35   $250.30  
  Purchase #7 $233.57   6.252%   $248.1728   $248.17   $248.15   $248.20  
  7 purchase totals = $856.56       $916.6937   $916.69   $916.70   $916.70