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	$144.74	10.406%	$159.8016	$159.80	$159.80	$159.80
Purchase #2	$183.97	3.482%	$190.3758	$190.38	$190.40	$190.40
Purchase #3	$106.71	5.640%	$112.7284	$112.73	$112.75	$112.70
Purchase #4	$215.77	8.346%	$233.7782	$233.78	$233.80	$233.80
Purchase #5	$51.35	11.136%	$57.0683	$57.07	$57.05	$57.10
Purchase #6	$250.69	11.501%	$279.5219	$279.52	$279.50	$279.50
Purchase #7	$162.87	13.856%	$185.4373	$185.44	$185.45	$185.40
7 purchase totals =	$1,116.10		$1,218.7115	$1,218.72	$1,218.75	$1,218.70