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	$112.38	13.460%	$127.5063	$127.51	$127.50	$127.50
Purchase #2	$91.31	13.183%	$103.3474	$103.35	$103.35	$103.30
Purchase #3	$237.34	8.167%	$256.7236	$256.72	$256.70	$256.70
Purchase #4	$102.37	3.377%	$105.827	$105.83	$105.85	$105.80
Purchase #5	$233.37	8.295%	$252.728	$252.73	$252.75	$252.70
Purchase #6	$240.59	6.248%	$255.6221	$255.62	$255.60	$255.60
Purchase #7	$132.46	11.333%	$147.4717	$147.47	$147.45	$147.50
7 purchase totals =	$1,149.82		$1,249.2261	$1,249.23	$1,249.20	$1,249.10