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	$168.37	6.590%	$179.4656	$179.47	$179.45	$179.50
Purchase #2	$238.78	11.739%	$266.8104	$266.81	$266.80	$266.80
Purchase #3	$134.54	12.556%	$151.4328	$151.43	$151.45	$151.40
Purchase #4	$167.49	12.232%	$187.9774	$187.98	$188.00	$188.00
Purchase #5	$77.52	6.852%	$82.8317	$82.83	$82.85	$82.80
Purchase #6	$171.84	5.642%	$181.5352	$181.54	$181.55	$181.50
Purchase #7	$172.60	8.472%	$187.2227	$187.22	$187.20	$187.20
7 purchase totals =	$1,131.14		$1,237.2758	$1,237.28	$1,237.30	$1,237.20