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	$97.54	4.871%	$102.2912	$102.29	$102.30	$102.30
Purchase #2	$99.74	11.716%	$111.4255	$111.43	$111.45	$111.40
Purchase #3	$33.81	6.136%	$35.8846	$35.88	$35.90	$35.90
Purchase #4	$126.71	8.212%	$137.1154	$137.12	$137.10	$137.10
Purchase #5	$9.92	10.281%	$10.9399	$10.94	$10.95	$10.90
Purchase #6	$39.81	9.104%	$43.4343	$43.43	$43.45	$43.40
Purchase #7	$133.93	5.449%	$141.2278	$141.23	$141.25	$141.20
7 purchase totals =	$541.46		$582.3187	$582.32	$582.40	$582.20