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	$16.71	8.659%	$18.1569	$18.16	$18.15	$18.20
Purchase #2	$111.84	4.239%	$116.5809	$116.58	$116.60	$116.60
Purchase #3	$232.73	13.531%	$264.2207	$264.22	$264.20	$264.20
Purchase #4	$233.75	9.155%	$255.1498	$255.15	$255.15	$255.10
Purchase #5	$230.54	4.532%	$240.9881	$240.99	$241.00	$241.00
Purchase #6	$131.54	10.373%	$145.1846	$145.18	$145.20	$145.20
Purchase #7	$97.94	7.801%	$105.5803	$105.58	$105.60	$105.60
7 purchase totals =	$1,055.05		$1,145.8613	$1,145.86	$1,145.90	$1,145.90