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 $56.57   12.267%   $63.5094   $63.51   $63.50   $63.50  
  Purchase #2 $113.99   3.864%   $118.3946   $118.39   $118.40   $118.40  
  Purchase #3 $119.32   4.166%   $124.2909   $124.29   $124.30   $124.30  
  Purchase #4 $190.28   10.513%   $210.2841   $210.28   $210.30   $210.30  
  Purchase #5 $87.67   10.397%   $96.785   $96.79   $96.80   $96.80  
  Purchase #6 $57.81   11.555%   $64.4899   $64.49   $64.50   $64.50  
  Purchase #7 $169.71   13.293%   $192.2696   $192.27   $192.25   $192.30  
  7 purchase totals = $795.35       $870.0235   $870.02   $870.05   $870.10