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 $236.95   11.255%   $263.6187   $263.62   $263.60   $263.60  
  Purchase #2 $19.33   8.194%   $20.9139   $20.91   $20.90   $20.90  
  Purchase #3 $41.39   5.355%   $43.6064   $43.61   $43.60   $43.60  
  Purchase #4 $151.65   8.398%   $164.3856   $164.39   $164.40   $164.40  
  Purchase #5 $205.37   3.351%   $212.2519   $212.25   $212.25   $212.30  
  Purchase #6 $5.68   6.678%   $6.0593   $6.06   $6.05   $6.10  
  Purchase #7 $114.30   10.686%   $126.5141   $126.51   $126.50   $126.50  
  7 purchase totals = $774.67       $837.3499   $837.35   $837.30   $837.40