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	$20.40	3.464%	$21.1067	$21.11	$21.10	$21.10
Purchase #2	$56.46	10.749%	$62.5289	$62.53	$62.55	$62.50
Purchase #3	$160.72	4.200%	$167.4702	$167.47	$167.45	$167.50
Purchase #4	$53.46	3.156%	$55.1472	$55.15	$55.15	$55.10
Purchase #5	$213.55	4.443%	$223.038	$223.04	$223.05	$223.00
Purchase #6	$23.51	5.699%	$24.8498	$24.85	$24.85	$24.80
Purchase #7	$249.40	9.614%	$273.3773	$273.38	$273.40	$273.40
7 purchase totals =	$777.50		$827.5181	$827.53	$827.55	$827.40