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	$99.43	12.372%	$111.7315	$111.73	$111.75	$111.70
Purchase #2	$108.30	9.102%	$118.1575	$118.16	$118.15	$118.20
Purchase #3	$116.35	9.579%	$127.4952	$127.50	$127.50	$127.50
Purchase #4	$156.70	11.774%	$175.1499	$175.15	$175.15	$175.10
Purchase #5	$122.57	5.241%	$128.9939	$128.99	$129.00	$129.00
Purchase #6	$86.68	12.222%	$97.274	$97.27	$97.25	$97.30
Purchase #7	$40.89	6.219%	$43.4329	$43.43	$43.45	$43.40
7 purchase totals =	$730.92		$802.2349	$802.23	$802.25	$802.20