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	$178.65	4.495%	$186.6803	$186.68	$186.70	$186.70
Purchase #2	$215.90	8.113%	$233.416	$233.42	$233.40	$233.40
Purchase #3	$18.76	11.531%	$20.9232	$20.92	$20.90	$20.90
Purchase #4	$180.58	13.807%	$205.5127	$205.51	$205.50	$205.50
Purchase #5	$143.49	8.333%	$155.447	$155.45	$155.45	$155.40
Purchase #6	$139.72	10.167%	$153.9253	$153.93	$153.95	$153.90
Purchase #7	$247.36	3.288%	$255.4932	$255.49	$255.50	$255.50
7 purchase totals =	$1,124.46		$1,211.3977	$1,211.40	$1,211.40	$1,211.30