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 $183.66   12.843%   $207.2475   $207.25   $207.25   $207.20  
  Purchase #2 $210.44   9.727%   $230.9095   $230.91   $230.90   $230.90  
  Purchase #3 $127.59   11.192%   $141.8699   $141.87   $141.85   $141.90  
  Purchase #4 $74.26   6.840%   $79.3394   $79.34   $79.35   $79.30  
  Purchase #5 $48.66   6.454%   $51.8005   $51.80   $51.80   $51.80  
  Purchase #6 $164.94   3.493%   $170.7014   $170.70   $170.70   $170.70  
  Purchase #7 $101.78   12.375%   $114.3753   $114.38   $114.40   $114.40  
  7 purchase totals = $911.33       $996.2435   $996.25   $996.25   $996.20