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	$161.42	11.749%	$180.3852	$180.39	$180.40	$180.40
Purchase #2	$34.68	9.245%	$37.8862	$37.89	$37.90	$37.90
Purchase #3	$219.37	11.738%	$245.1197	$245.12	$245.10	$245.10
Purchase #4	$239.45	5.136%	$251.7482	$251.75	$251.75	$251.70
Purchase #5	$173.39	3.287%	$179.0893	$179.09	$179.10	$179.10
Purchase #6	$96.64	6.503%	$102.9245	$102.92	$102.90	$102.90
Purchase #7	$111.65	10.223%	$123.064	$123.06	$123.05	$123.10
7 purchase totals =	$1,036.60		$1,120.2171	$1,120.22	$1,120.20	$1,120.20