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	$129.88	7.517%	$139.6431	$139.64	$139.65	$139.60
Purchase #2	$97.90	13.424%	$111.0421	$111.04	$111.05	$111.00
Purchase #3	$22.99	3.615%	$23.8211	$23.82	$23.80	$23.80
Purchase #4	$113.76	12.192%	$127.6296	$127.63	$127.65	$127.60
Purchase #5	$153.66	4.294%	$160.2582	$160.26	$160.25	$160.30
Purchase #6	$9.91	7.106%	$10.6142	$10.61	$10.60	$10.60
Purchase #7	$60.59	3.467%	$62.6907	$62.69	$62.70	$62.70
7 purchase totals =	$588.69		$635.6990	$635.69	$635.70	$635.60