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	$225.29	6.323%	$239.5351	$239.54	$239.55	$239.50
Purchase #2	$176.59	6.334%	$187.7752	$187.78	$187.80	$187.80
Purchase #3	$235.56	13.121%	$266.4678	$266.47	$266.45	$266.50
Purchase #4	$145.28	9.233%	$158.6937	$158.69	$158.70	$158.70
Purchase #5	$144.82	7.241%	$155.3064	$155.31	$155.30	$155.30
Purchase #6	$83.76	3.361%	$86.5752	$86.58	$86.60	$86.60
Purchase #7	$98.27	7.476%	$105.6167	$105.62	$105.60	$105.60
7 purchase totals =	$1,109.57		$1,199.9701	$1,199.99	$1,200.00	$1,200.00