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	$19.51	12.628%	$21.9737	$21.97	$21.95	$22.00
Purchase #2	$116.85	5.771%	$123.5934	$123.59	$123.60	$123.60
Purchase #3	$133.38	10.446%	$147.3129	$147.31	$147.30	$147.30
Purchase #4	$23.53	8.568%	$25.5461	$25.55	$25.55	$25.50
Purchase #5	$122.65	11.239%	$136.4346	$136.43	$136.45	$136.40
Purchase #6	$114.97	11.105%	$127.7374	$127.74	$127.75	$127.70
Purchase #7	$141.73	11.825%	$158.4896	$158.49	$158.50	$158.50
7 purchase totals =	$672.62		$741.0877	$741.08	$741.10	$741.00