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 $66.27   11.329%   $73.7777   $73.78   $73.80   $73.80  
  Purchase #2 $127.71   10.652%   $141.3137   $141.31   $141.30   $141.30  
  Purchase #3 $196.84   3.593%   $203.9125   $203.91   $203.90   $203.90  
  Purchase #4 $124.45   7.343%   $133.5884   $133.59   $133.60   $133.60  
  Purchase #5 $71.88   6.762%   $76.7405   $76.74   $76.75   $76.70  
  Purchase #6 $239.38   12.274%   $268.7615   $268.76   $268.75   $268.80  
  Purchase #7 $160.44   10.411%   $177.1434   $177.14   $177.15   $177.10  
  7 purchase totals = $986.97       $1,075.2377   $1,075.23   $1,075.25   $1,075.20