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 $55.73   12.488%   $62.6896   $62.69   $62.70   $62.70  
  Purchase #2 $146.41   7.260%   $157.0394   $157.04   $157.05   $157.00  
  Purchase #3 $230.75   7.462%   $247.9686   $247.97   $247.95   $248.00  
  Purchase #4 $163.30   6.476%   $173.8753   $173.88   $173.90   $173.90  
  Purchase #5 $54.70   4.748%   $57.2972   $57.30   $57.30   $57.30  
  Purchase #6 $158.72   8.637%   $172.4286   $172.43   $172.45   $172.40  
  Purchase #7 $119.66   3.689%   $124.0743   $124.07   $124.05   $124.10  
  7 purchase totals = $929.27       $995.3730   $995.38   $995.40   $995.40