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	$87.87	13.699%	$99.9073	$99.91	$99.90	$99.90
Purchase #2	$161.31	7.830%	$173.9406	$173.94	$173.95	$173.90
Purchase #3	$156.93	9.549%	$171.9152	$171.92	$171.90	$171.90
Purchase #4	$141.71	10.531%	$156.6335	$156.63	$156.65	$156.60
Purchase #5	$205.97	8.615%	$223.7143	$223.71	$223.70	$223.70
Purchase #6	$209.28	10.168%	$230.5596	$230.56	$230.55	$230.60
Purchase #7	$118.49	11.833%	$132.5109	$132.51	$132.50	$132.50
7 purchase totals =	$1,081.56		$1,189.1814	$1,189.18	$1,189.15	$1,189.10