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	$81.63	10.448%	$90.1587	$90.16	$90.15	$90.20
Purchase #2	$18.31	4.472%	$19.1288	$19.13	$19.15	$19.10
Purchase #3	$62.42	9.453%	$68.3206	$68.32	$68.30	$68.30
Purchase #4	$126.86	8.121%	$137.1623	$137.16	$137.15	$137.20
Purchase #5	$36.71	11.624%	$40.9772	$40.98	$41.00	$41.00
Purchase #6	$128.31	13.431%	$145.5433	$145.54	$145.55	$145.50
Purchase #7	$67.80	6.509%	$72.2131	$72.21	$72.20	$72.20
7 purchase totals =	$522.04		$573.5040	$573.50	$573.50	$573.50