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	$150.89	13.712%	$171.58	$171.58	$171.60	$171.60
Purchase #2	$27.64	5.450%	$29.1464	$29.15	$29.15	$29.10
Purchase #3	$143.49	4.284%	$149.6371	$149.64	$149.65	$149.60
Purchase #4	$37.59	10.456%	$41.5204	$41.52	$41.50	$41.50
Purchase #5	$194.46	10.485%	$214.8491	$214.85	$214.85	$214.80
Purchase #6	$14.67	12.539%	$16.5095	$16.51	$16.50	$16.50
Purchase #7	$157.89	9.156%	$172.3464	$172.35	$172.35	$172.30
7 purchase totals =	$726.63		$795.5889	$795.60	$795.60	$795.40