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	$38.99	4.433%	$40.7184	$40.72	$40.70	$40.70
Purchase #2	$103.86	11.820%	$116.1363	$116.14	$116.15	$116.10
Purchase #3	$104.50	13.754%	$118.8729	$118.87	$118.85	$118.90
Purchase #4	$243.33	3.813%	$252.6082	$252.61	$252.60	$252.60
Purchase #5	$159.27	5.209%	$167.5664	$167.57	$167.55	$167.60
Purchase #6	$139.96	8.483%	$151.8328	$151.83	$151.85	$151.80
Purchase #7	$141.90	12.714%	$159.9412	$159.94	$159.95	$159.90
7 purchase totals =	$931.81		$1,007.6762	$1,007.68	$1,007.65	$1,007.60