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	$126.40	13.867%	$143.9279	$143.93	$143.95	$143.90
Purchase #2	$20.94	10.413%	$23.1205	$23.12	$23.10	$23.10
Purchase #3	$137.42	6.457%	$146.2932	$146.29	$146.30	$146.30
Purchase #4	$62.82	8.210%	$67.9775	$67.98	$68.00	$68.00
Purchase #5	$203.84	13.803%	$231.976	$231.98	$232.00	$232.00
Purchase #6	$111.52	10.504%	$123.2341	$123.23	$123.25	$123.20
Purchase #7	$76.46	3.220%	$78.922	$78.92	$78.90	$78.90
7 purchase totals =	$739.40		$815.4512	$815.45	$815.50	$815.40