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	$138.58	10.523%	$153.1628	$153.16	$153.15	$153.20
Purchase #2	$20.98	5.358%	$22.1041	$22.10	$22.10	$22.10
Purchase #3	$181.50	10.355%	$200.2943	$200.29	$200.30	$200.30
Purchase #4	$140.37	10.732%	$155.4345	$155.43	$155.45	$155.40
Purchase #5	$170.65	4.401%	$178.1603	$178.16	$178.15	$178.20
Purchase #6	$111.61	6.499%	$118.8635	$118.86	$118.85	$118.90
Purchase #7	$51.38	7.777%	$55.3758	$55.38	$55.40	$55.40
7 purchase totals =	$815.07		$883.3953	$883.38	$883.40	$883.50