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	$50.28	11.174%	$55.8983	$55.90	$55.90	$55.90
Purchase #2	$196.73	9.201%	$214.8311	$214.83	$214.85	$214.80
Purchase #3	$105.64	5.857%	$111.8273	$111.83	$111.85	$111.80
Purchase #4	$78.42	7.825%	$84.5564	$84.56	$84.55	$84.60
Purchase #5	$39.25	11.624%	$43.8124	$43.81	$43.80	$43.80
Purchase #6	$143.57	12.310%	$161.2435	$161.24	$161.25	$161.20
Purchase #7	$106.79	8.797%	$116.1843	$116.18	$116.20	$116.20
7 purchase totals =	$720.68		$788.3533	$788.35	$788.40	$788.30