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 $62.58   8.821%   $68.1002   $68.10   $68.10   $68.10  
  Purchase #2 $222.79   11.868%   $249.2307   $249.23   $249.25   $249.20  
  Purchase #3 $12.47   13.866%   $14.1991   $14.20   $14.20   $14.20  
  Purchase #4 $114.56   10.840%   $126.9783   $126.98   $127.00   $127.00  
  Purchase #5 $130.66   10.545%   $144.4381   $144.44   $144.45   $144.40  
  Purchase #6 $160.44   9.701%   $176.0043   $176.00   $176.00   $176.00  
  Purchase #7 $129.68   7.643%   $139.5914   $139.59   $139.60   $139.60  
  7 purchase totals = $833.18       $918.5421   $918.54   $918.60   $918.50