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 $7.32   13.663%   $8.3201   $8.32   $8.30   $8.30  
  Purchase #2 $118.72   13.169%   $134.3542   $134.35   $134.35   $134.40  
  Purchase #3 $46.53   3.293%   $48.0622   $48.06   $48.05   $48.10  
  Purchase #4 $85.62   12.659%   $96.4586   $96.46   $96.45   $96.50  
  Purchase #5 $146.61   5.226%   $154.2718   $154.27   $154.25   $154.30  
  Purchase #6 $248.28   13.485%   $281.7606   $281.76   $281.75   $281.80  
  Purchase #7 $167.46   4.252%   $174.5804   $174.58   $174.60   $174.60  
  7 purchase totals = $820.54       $897.8079   $897.80   $897.75   $898.00