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 $196.90   4.145%   $205.0615   $205.06   $205.05   $205.10  
  Purchase #2 $177.38   4.622%   $185.5785   $185.58   $185.60   $185.60  
  Purchase #3 $50.84   8.163%   $54.9901   $54.99   $55.00   $55.00  
  Purchase #4 $148.95   11.379%   $165.899   $165.90   $165.90   $165.90  
  Purchase #5 $76.59   12.581%   $86.2258   $86.23   $86.25   $86.20  
  Purchase #6 $230.36   7.816%   $248.3649   $248.36   $248.35   $248.40  
  Purchase #7 $235.50   13.847%   $268.1097   $268.11   $268.10   $268.10  
  7 purchase totals = $1,116.52       $1,214.2295   $1,214.23   $1,214.25   $1,214.30