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 $75.96   11.175%   $84.4485   $84.45   $84.45   $84.40  
  Purchase #2 $109.65   4.873%   $114.9932   $114.99   $115.00   $115.00  
  Purchase #3 $32.86   9.863%   $36.101   $36.10   $36.10   $36.10  
  Purchase #4 $113.94   11.499%   $127.042   $127.04   $127.05   $127.00  
  Purchase #5 $236.69   12.158%   $265.4668   $265.47   $265.45   $265.50  
  Purchase #6 $139.68   8.625%   $151.7274   $151.73   $151.75   $151.70  
  Purchase #7 $11.58   4.801%   $12.136   $12.14   $12.15   $12.10  
  7 purchase totals = $720.36       $791.9149   $791.92   $791.95   $791.80