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	$10.95	13.271%	$12.4032	$12.40	$12.40	$12.40
Purchase #2	$249.25	10.855%	$276.3061	$276.31	$276.30	$276.30
Purchase #3	$9.64	12.346%	$10.8302	$10.83	$10.85	$10.80
Purchase #4	$91.39	3.751%	$94.818	$94.82	$94.80	$94.80
Purchase #5	$31.80	5.259%	$33.4724	$33.47	$33.45	$33.50
Purchase #6	$170.35	8.632%	$185.0546	$185.05	$185.05	$185.10
Purchase #7	$242.42	8.233%	$262.3784	$262.38	$262.40	$262.40
7 purchase totals =	$805.80		$875.2629	$875.26	$875.25	$875.30