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	$242.32	5.793%	$256.3576	$256.36	$256.35	$256.40
Purchase #2	$237.61	12.655%	$267.6795	$267.68	$267.70	$267.70
Purchase #3	$144.87	4.504%	$151.3949	$151.39	$151.40	$151.40
Purchase #4	$147.80	4.607%	$154.6091	$154.61	$154.60	$154.60
Purchase #5	$109.59	4.709%	$114.7506	$114.75	$114.75	$114.80
Purchase #6	$71.39	8.165%	$77.219	$77.22	$77.20	$77.20
Purchase #7	$117.96	11.167%	$131.1326	$131.13	$131.15	$131.10
7 purchase totals =	$1,071.54		$1,153.1433	$1,153.14	$1,153.15	$1,153.20