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	$183.76	5.565%	$193.9862	$193.99	$194.00	$194.00
Purchase #2	$162.36	6.241%	$172.4929	$172.49	$172.50	$172.50
Purchase #3	$32.41	8.227%	$35.0764	$35.08	$35.10	$35.10
Purchase #4	$103.51	7.739%	$111.5206	$111.52	$111.50	$111.50
Purchase #5	$17.72	3.553%	$18.3496	$18.35	$18.35	$18.30
Purchase #6	$17.71	6.538%	$18.8679	$18.87	$18.85	$18.90
Purchase #7	$22.33	3.558%	$23.1245	$23.12	$23.10	$23.10
7 purchase totals =	$539.80		$573.4181	$573.42	$573.40	$573.40