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	$18.86	11.805%	$21.0864	$21.09	$21.10	$21.10
Purchase #2	$87.76	5.662%	$92.729	$92.73	$92.75	$92.70
Purchase #3	$233.50	3.849%	$242.4874	$242.49	$242.50	$242.50
Purchase #4	$113.38	4.868%	$118.8993	$118.90	$118.90	$118.90
Purchase #5	$121.96	4.634%	$127.6116	$127.61	$127.60	$127.60
Purchase #6	$209.91	7.714%	$226.1025	$226.10	$226.10	$226.10
Purchase #7	$157.47	9.830%	$172.9493	$172.95	$172.95	$172.90
7 purchase totals =	$942.84		$1,001.8655	$1,001.87	$1,001.90	$1,001.80