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	$97.57	10.489%	$107.8041	$107.80	$107.80	$107.80
Purchase #2	$115.78	7.603%	$124.5828	$124.58	$124.60	$124.60
Purchase #3	$105.29	6.415%	$112.0444	$112.04	$112.05	$112.00
Purchase #4	$78.39	4.617%	$82.0093	$82.01	$82.00	$82.00
Purchase #5	$181.42	4.748%	$190.0338	$190.03	$190.05	$190.00
Purchase #6	$137.50	6.788%	$146.8335	$146.83	$146.85	$146.80
Purchase #7	$112.75	12.852%	$127.2406	$127.24	$127.25	$127.20
7 purchase totals =	$828.70		$890.5485	$890.53	$890.60	$890.40