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 $226.92   9.558%   $248.609   $248.61   $248.60   $248.60  
  Purchase #2 $131.99   6.264%   $140.2579   $140.26   $140.25   $140.30  
  Purchase #3 $155.47   3.548%   $160.9861   $160.99   $161.00   $161.00  
  Purchase #4 $103.54   13.410%   $117.4247   $117.42   $117.40   $117.40  
  Purchase #5 $111.61   10.215%   $123.011   $123.01   $123.00   $123.00  
  Purchase #6 $115.67   8.409%   $125.3967   $125.40   $125.40   $125.40  
  Purchase #7 $40.71   13.656%   $46.2694   $46.27   $46.25   $46.30  
  7 purchase totals = $885.91       $961.9548   $961.96   $961.90   $962.00