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	$186.55	12.742%	$210.3202	$210.32	$210.30	$210.30
Purchase #2	$230.95	9.510%	$252.9133	$252.91	$252.90	$252.90
Purchase #3	$127.81	10.201%	$140.8479	$140.85	$140.85	$140.80
Purchase #4	$219.56	8.404%	$238.0118	$238.01	$238.00	$238.00
Purchase #5	$83.39	7.707%	$89.8169	$89.82	$89.80	$89.80
Purchase #6	$69.92	10.298%	$77.1204	$77.12	$77.10	$77.10
Purchase #7	$204.85	4.476%	$214.0191	$214.02	$214.00	$214.00
7 purchase totals =	$1,123.03		$1,223.0496	$1,223.05	$1,222.95	$1,222.90