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	$178.37	3.109%	$183.9155	$183.92	$183.90	$183.90
Purchase #2	$137.63	4.108%	$143.2838	$143.28	$143.30	$143.30
Purchase #3	$109.83	11.613%	$122.5846	$122.58	$122.60	$122.60
Purchase #4	$103.52	8.151%	$111.9579	$111.96	$111.95	$112.00
Purchase #5	$114.80	4.394%	$119.8443	$119.84	$119.85	$119.80
Purchase #6	$87.73	9.319%	$95.9056	$95.91	$95.90	$95.90
Purchase #7	$157.87	9.479%	$172.8345	$172.83	$172.85	$172.80
7 purchase totals =	$889.75		$950.3262	$950.32	$950.35	$950.30