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	$138.89	13.739%	$157.9721	$157.97	$157.95	$158.00
Purchase #2	$18.43	10.866%	$20.4326	$20.43	$20.45	$20.40
Purchase #3	$211.34	9.263%	$230.9164	$230.92	$230.90	$230.90
Purchase #4	$241.54	9.138%	$263.6119	$263.61	$263.60	$263.60
Purchase #5	$230.88	4.784%	$241.9253	$241.93	$241.95	$241.90
Purchase #6	$13.71	10.761%	$15.1853	$15.19	$15.20	$15.20
Purchase #7	$238.53	6.862%	$254.8979	$254.90	$254.90	$254.90
7 purchase totals =	$1,093.32		$1,184.9415	$1,184.95	$1,184.95	$1,184.90