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	$177.42	5.420%	$187.0362	$187.04	$187.05	$187.00
Purchase #2	$241.45	13.456%	$273.9395	$273.94	$273.95	$273.90
Purchase #3	$127.96	8.868%	$139.3075	$139.31	$139.30	$139.30
Purchase #4	$143.57	10.246%	$158.2802	$158.28	$158.30	$158.30
Purchase #5	$146.61	8.808%	$159.5234	$159.52	$159.50	$159.50
Purchase #6	$233.85	6.811%	$249.7775	$249.78	$249.80	$249.80
Purchase #7	$212.49	9.867%	$233.4564	$233.46	$233.45	$233.50
7 purchase totals =	$1,283.35		$1,401.3207	$1,401.33	$1,401.35	$1,401.30