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	$230.61	11.556%	$257.2593	$257.26	$257.25	$257.30
Purchase #2	$164.99	9.536%	$180.7234	$180.72	$180.70	$180.70
Purchase #3	$136.52	12.792%	$153.9836	$153.98	$154.00	$154.00
Purchase #4	$167.72	10.609%	$185.5134	$185.51	$185.50	$185.50
Purchase #5	$168.27	13.216%	$190.5086	$190.51	$190.50	$190.50
Purchase #6	$39.58	4.375%	$41.3116	$41.31	$41.30	$41.30
Purchase #7	$130.60	10.204%	$143.9264	$143.93	$143.95	$143.90
7 purchase totals =	$1,038.29		$1,153.2263	$1,153.22	$1,153.20	$1,153.20